Trends in seasonal precipitation and temperature in Slovenia during 1951–2007

A quality-controlled and enhanced database of 38 temperature and 52 precipitation stations was developed for Slovenia, a transitional area between Mediterranean, Alpine and continental climatic regimes, covering the period 1951–2007. Mean annual temperatures significantly increased in nearly all of Slovenia (except western areas) at rates between 0.15 and 0.36 °C/decade. Warming was most intense strongest in summer and spring in north-eastern Slovenia (0.3–0.4 °C/decade) and weakest in autumn. Precipitation trends were heterogeneous. Annual precipitation decreased significantly in the north-western part, at 3–6 % per decade. During spring and summer, decrease in rainfall by 3–6 % was detected in western Slovenia. No significant trends were found for the autumn season. In winter, precipitation decreased, by 3–12 % per decade, in particular in north-western Slovenia. As observed also elsewhere in Central Europe, changes in large-scale atmospheric circulation patterns may have contributed to the observed long-term warming and drying in Slovenia. However, the strong warming in summer and spring, that is almost twice the trend observed in neighbouring countries, could be enhanced by drier soils caused by the decrease in winter precipitation in Slovenia.     

Spatio-temporal analysis of climatic variables in the western part of Bangladesh

Monitoring and detecting trends of climatic variables like rainfall and temperature are essential for agricultural developments in the context of climate change. The present study has detected trends in annual and cropping seasonal rainfall and temperature data for the period of 1961–2011 using Mann–Kendall (MK) test, Spearman’s rho (SR) test and modified Mann–Kendall test that has been applied to the significant lag-1 serial correlated time series data, and slope has been estimated using Sen’s Slope estimator for twelve meteorological stations located in the western part of Bangladesh covering about 41 % of the country. Almost 71 % trends explored by MK test in annual rainfall are statistically insignificant, and SR test also complies it. The spatial distribution of rainfall trend shows insignificant positive trends in major part of the area. Significant positive trends both by MK test and by SR test at 95 % confidence levels are observed at rates of 8.56, 11.15 and 13.66 mm/year at Dinajpur, Rangpur and Khepupara stations, respectively, and the Kharif season rainfall of these stations also shows significant increasing trends except Dinajpur. On the other hand, significant decreasing trends in annual rainfall are found at Bhola (?11.67 mm/year) and Rajshahi (?5.951 mm/year) stations and decreasing trends in rainfall dominated the Pre-Kharif season over the area. But, 83.33 % of the stations show rising trends in annual mean temperature with significant positive trends (as observed by both MK test and SR test) at Rangpur, Bogra, Faridpur, Jessore and Bhola stations where the rate of changes vary from 0.013 °C/year at Faridpur to 0.08 °C/year at Bhola. Most of the trends in Rabi and Pre-Kharif seasons of mean temperatures are not statistically significant. However, all stations except Barisal show significant rising trends in temperature in Kharif season. To cope with this changing pattern of rainfall and temperature, effective adaptation strategies should be taken to keep up the agricultural production that is related to livelihood of the most people and to ensure the country’s food security.     

Spatial pattern of recent rainfall trends in Serbia (1961–2009)

This paper examines a spatial pattern of annual, seasonal and monthly rainfall trends in Serbia. The study used data from 63 weather stations between the period of 1961–2009. The rainfall series was examined by applying the nonparametric method of the Mann–Kendall test and Sen’s method to determine the significance and magnitude of the trends. Significant trends have not been detected for the whole country at an annual scale. Seasonal trends at the confidence level of 97.5 %, however, indicate a slight decrease in winter (5 stations out of 63) and spring (7 stations out of 63) precipitation and an increase in autumn precipitation (10 stations out of 63). Results for monthly rainfall trends also generally showed a nonsignificant trend with the exception of a negative trend in May (6 stations out of 63) and positive trend for October (9 stations out of 63). Calculated global autocorrelation statistics (Moran’s I) indicate a random spatial pattern of rainfall trends on annual, seasonal and monthly timescales with exceptions for March, June and November. Overall, results suggest that only weak, mostly nonsignificant trends are present in Serbia in the period 1961–2009.     

Quantifying fluctuations in winter productive cropped area in the Central Indian Highlands

The Central Indian Highland landscape (CIHL) represents a complex, diverse, and highly human-modified system. Nearly half the landscape is cropland, yet it hosts 21 protected areas surrounded and connected by forests. Changing farming practices with increasing access to irrigation might alter this intensifying landscape in the near future particularly in light of weather variability. We analyzed a decade of remote sensing data for cropping patterns and climatic factors combined with census data for irrigation and demographic factors to understand winter cropping trajectories in the CIHL. We quantified ‘productive cropped area’ (PCA), defined as the area with planted crop that is green at the peak of the winter growing season. We find three primary trajectories in PCA—increasing, fluctuating, and decreasing. The most dominant trend is fluctuating PCA in two-thirds of the districts, ranging from ~2.11 million to ~3.73 million ha between 2001 and 2013, which is associated with village-level access to irrigation and local labor dynamics. In 58 % of all districts, clay soils were associated with winter cropping (p < 0.05). Increasing irrigation is associated with increased winter PCA in most (94 %) districts (p < 0.00001). We find strong negative association between PCA and land surface temperature (LST) in most (66 %) districts (p < 0.01). LST closely corresponds to daytime mean air temperature (p < 0.001) for available meteorological stations. Fine-scale meteorological and socioeconomic data, however, are needed to further disentangle impacts of these factors on PCA in this landscape.     

Precipitation-driven decrease in wildfires in British Columbia

Trends of summer precipitation and summer temperature and their influence on trends in summer drought and area burned in British Columbia (BC) were investigated for the period 1920–2000. The complexity imposed by topography was taken into account by incorporating high spatial resolution climate and fire data. Considerable regional variation in trends and in climate–fire relationships was observed. A weak but significant increase in summer temperature was detected in northeastern and coastal BC, whereas summer precipitation increased significantly in all regions—by up to 45.9 %. A significant decrease in province-wide area burned and at the level of sub-units was strongly related to increasing precipitation, more so than to changing temperature or drought severity. A stronger dependence of area burned on precipitation, a variable difficult to predict, implies that projected changes in future area burned in this region may yield higher uncertainties than in regions where temperature is predominantly the limiting factor for fire activity. We argue that analyses of fire–climate relationships must be undertaken at a sufficiently high resolution such that spatial variability in limiting factors on area burned like precipitation, temperature, and drought is captured within units.     

Sensitivity of typical Mediterranean crops to past and future evolution of seasonal temperature and precipitation in Apulia

The region of Apulia, which is located in the south-east tip of the Italian Peninsula, has a typical Mediterranean climate with mild winters and hot-dry summers. Agriculture, an important sector of its economy, is potentially threatened by future climate change. This study describes the evolution of seasonal temperature and precipitation from the recent past to the next decades and estimates future potential impacts of climate change on three main agricultural products: wine, wheat and olives. Analysis is based on instrumental data, on an ensemble of climate projections and on a linear regression model linking these three agricultural products to seasonal values of temperature and precipitation. In Apulia, precipitation and temperature time series show trends toward warmer and marginally drier conditions during the whole analyzed (1951–2005) period: 0.18 °C/decade in mean annual minimum temperature and ?14.9 mm/decade in the annual total precipitation. Temperature trends have been progressively increasing and rates of change have become noticeably more intense during the last 25 years of the twentieth century. Model simulations are consistent with observed trends for the period 1951–2000 and show a large acceleration of the warming rate in the period 2001–2050 with respect to the period 1951–2000. Further, in the period 2001–2050, simulations show a decrease in precipitation, which was not present in the previous 50 years. Wine production, wheat and olive harvest records show large inter-annual variability with statistically significant links to seasonal temperature and precipitation, whose strength, however, strongly depends on the considered variables. Linear regression analysis shows that seasonal temperature and precipitation variability explains a small, but not negligible, fraction of the inter-annual variability of these crops (40, 18, 9 % for wine, olives and wheat, respectively). Results (which consider no adaptation of crops and no fertilization effect of CO₂) suggest that evolution of these seasonal climate variables in the first half of the twenty-first century could decrease all considered variables. The most affected is wine production (?20 ÷ ?26 %). The effect is relevant also on harvested olives (?8 ÷ ?19 %) and negligible on harvested wheat (?4 ÷ ?1 %).     

西南地区极端降水的时空变化特征

西南地区是我国山地灾害最为严重的区域之一，而短时极端降水则是山地灾害成灾演化的关键控制因素。以西南地区1960~2011年110个气象站的逐日降水量资料为基础，通过建立起超门限峰值序列(POT)，结合GIS空间分析技术与线性倾向估计、Mann Kendall趋势检验、Morlet小波分析等方法，研究了西南地区极端降水事件的时空变化规律。结果发现：20世纪60年代以来，西南地区极端降水频数有增加趋势，速率为0017/10 a，极端降水量在总降水量中所占的比重不断增加，增幅为0.638%/10a；西南地区极端降水频数的变化在年代际间存在显著的区域增减差异，增加的区域主要呈现出斑块状分布，而减少的区域则呈现出较明显的条带状分布；云南西南部、贵州大部和四川盆地中部3个区域是极端降水频发区，而川滇交界处的元谋-会理一带和四川盆地北部山区则较少发生极端降水；季风期极端降水频数呈现出明显的增加趋势，速率为0031次/10 a，非季风期极端降水频数则呈现出减少的趋势，速率为-0014次/10 a；季风期和年极端降水频数均没有明显的突变年份，非季风期存在3个突变点，分别是1969、1983和1994年；季风期与年极端降水存在27、15和7 a时间尺度上的周期性振荡，非季风期的周期性振荡则主要集中在27和12 a时间尺度上     

上海高温和低温气候变化特征及其影响因素

基于上海11个气象站逐日最高、最低气温、降水资料和西太平洋副热带高压(简称副高,下同)环流指数,分析了上海夏季高温和冬季低温的气候变化特征及其影响因素.结果表明,1873～2007年,上海高温日数表现为少-多-少-多的年代际变化,低温日数则表现为多-少的年代际变化.2001～2007年,上海年均高温日数、各级高温过程数和高温过程日数都最多,低温日数、低温过程数和低温过程日数都最少.1960～2007年,上海每年高温日数与当年夏季副高面积和强度指数显著正相关,低温日数与当年冬季副高面积和强度指数显著负相关.降水对上海极端气温有一定的缓解作用,上海高温日数与夏季降水量弱显著负相关,低温日数与冬季降水量显著负相关.上海高温过程数受城市化影响较大,其时间变化具有明显的城郊差异,低温过程数则受城市化影响较小.     

Assessment of climate change simulations over climate zones of Turkey

Projected climate change over Turkey has been analyzed by using the reference (1961–1990) and future (2071–2100) climate simulations produced by ICTP-RegCM3. Since examining Turkey as a single region could be misleading due to the existence of complex topography and different climatic regions, Turkey has been separated into seven climatic regions to evaluate the surface temperature and precipitation changes. Comparison of the reference simulation with observations was made spatially by using a monthly gridded data set and area-averaged surface data compiled from 114 meteorological stations for each climatic region of Turkey. In the future simulation, warming over Turkey’s climatic regions is in the range of 2–5 °C. Summer warming over western regions of Turkey is 3 °C higher than the winter warming. During winter, in the future simulation, precipitation decreases very significantly over southeastern Turkey (24 %), which covers most of the upstream of Euphrates and Tigris river basin. This projected decrease could be a major source of concern for Turkey and the neighboring countries. Our results indicate that a significant increase (48 %) in the autumn season precipitation is simulated over southeastern Turkey, which may help to offset the winter deficit and therefore reduce the net change during the annual cycle.     

青藏高原四季降水变化特征分析

利用青藏高原87个地面气象台站41年（1960～2000年）的月降水资料,并在Arcgis 9.0中通过Kriging插值方法对少数站点的缺测值进行了插补,用线性回归方法研究了高原四季降水量的变化趋势及区域上的差异。为了保证本研究的完整性,对高原年降水也做了相应分析。结果表明：（1）高原冬春两季降水量呈显著增加趋势。冬季雅鲁藏布江下游、春季高原东北部为降水减少区,高原其他区域均表现为增加;夏秋两季降水量基本保持不变,但夏季高原中部和川西降水减少,高原南部和北部降水表现为增加;秋季高原中部、南部降水增加,川西降水减少。（2）高原年降水呈显著增加趋势。在区域上高原南部大致以东经102度为界,该线以东降水减少,以西降水增加,且降水增加区域表现出随纬度的增加而递减的特征。高原中部、北部的年降水基本保持不变或微弱增加。     

Effect of temperature and precipitation on linear increment of <Emphasis Type="Italic">Sphagnum fuscum</Emphasis> and <Emphasis Type="Italic">S. magellanicum</Emphasis> in Western Siberia

The linear increment of Sphagnum fuscum and S. magellanicum in ombrotrophic mires of Western Siberia has been measured during two years over a transect about 2500 km long extending from forest–steppe to forest–tundra. Along the latitudinal gradient, the increment of both species has proved to be correlated with annual average air temperature and, in S. magellanicum, also with annual precipitation. The determinants of their growth differ between the southern, central, and northern parts of the study region. At the regional level, the annual and summer precipitation plays a more important role than the average air temperature. The increment of S. fuscum in the southern part is positively correlated with the amount of precipitation and negatively correlated with summer temperature, whereas the situation in the central part is inverse. In S. magellanicum, the linear increment is directly dependent on the annual average temperature and annual and summer precipitation in the south and on the annual and summer precipitation in the north of Western Siberia. The dynamics of linear growth of both species in bog pine forests during the growing season are similar: its rate is the highest in June, when the linear increment of S. fuscum and S. magellanicum amounts to 60 and 85% of the annual total, respectively.     

Effect of human use,season and habitat on ungulate density in Kanha Tiger Reserve,Madhya Pradesh,India

Conservation practitioners require strata specific, seasonal species densities for habitat management. Herein, we use stratified distance sampling in Kanha Tiger Reserve (KTR) with 200 spatial transects and an effort of 1200 km walk in the year 2013. Analysis was done to access (a) impact of human use and (b) effect of habitat and season on ungulate densities in KTR. While a single detection function for each species was used for estimating density within human-restricted core and multiple use buffer of KTR, species-specific seasonal detections were modelled for each habitat. Ungulate biomass was 4.8 times higher in the core area compared with the buffer zone. The core supported a herbivore density and biomass of 50 ± 4.80/km² and 26,806 ± 2573 kg/km², respectively. Chital were found to be most abundant, having a density of 30.1 ± 4.34/km² and contributing 33 % of the biomass with a habitat preference for grasslands (106 ± 39/km²) in summer and winter. Sambar had highest density (15.4 ± 3.34/km²) in bamboo-mixed habitat, in both seasons. Gaur contributed 39 % of the ungulate biomass and showed a seasonal shift in density from sal forests (9.65 ± 3.55/km²) in summer to miscellaneous forests (8.13 ± 1.94/km²) in winter. Barasingha were restricted to grasslands with similar summer and winter densities of 1.56 ± 0.76/km². Chousingha were rare (0.1 ± 0.04/km²), found mostly in miscellaneous forests and plateau grasslands. Grassland and bamboo-mixed forests supported 58 % of the total ungulate biomass. Management for an optimal habitat mosaic that maintains ungulate diversity, addresses the specific needs of endangered species and maximizes ungulate biomass is recommended.     

Seasonal changes in daily precipitation extremes in mainland Portugal from 1941 to 2007

This study aims mostly at understanding seasonal variations in the intensity, frequency and duration of extreme precipitation events in mainland Portugal. For this purpose, selected precipitation indices that mainly focus on extremes were calculated at the seasonal scale for daily data recorded in the period 1941–2007 at 57 meteorological stations scattered across the area. These indices were explored for trends at the local and regional levels. The results show that there are marked changes in precipitation indices at the seasonal scale. Trends in spring and autumn precipitation have opposite signals. In spring, statistically significant drying trends are found together with a reduction in extremes. In autumn, wetting trends are detected for all indices, although overall they are not significant at the 5 % level. In addition, the relationship between seasonal extreme precipitation indices and atmospheric large-scale modes of low-frequency variability is analysed by means of a seasonal correlation analysis. Four modes of low-frequency variability are explored. Results confirm that, over mainland Portugal, the North Atlantic Oscillation is one of the most important teleconnection patterns in any season and the mode of variability that has the greatest influence on precipitation extremes in the area, particularly in the winter and autumn.     

Hydrologic response to climate change and human activities in a subtropical coastal watershed of southeast China

It is essential to investigate hydrologic responses to climate change and human activities across different physiographic regions so as to formulate sound strategies for water resource management. Mann–Kendall, wavelet and geospatial analyses were coupled in this study, associated with ENSO indicators, flashiness index and baseflow index, in order to explore the hydrologic sensitivity to climate change and human activities in the Jiulong River Basin (JRB), a subtropical coastal watershed of southeast China. The results showed that the average annual precipitation presented an increasing trend (Z = 2.263, p = 0.024) and that this tendency has become weaker from estuary to inland in the JRB over the past 50 years. The annual frequency of rainstorm events increased from 3.4 to 5.2 days in the estuary and from 5.1 to 5.6 days in the West River, whereas it decreased from 6.0 to 5.5 days in the North River from 1954 to 2010. The 10-year average streamflow during 2001–2010 in the North River and West River decreased by 9.2 and 6.7 %, respectively, compared to the average annual streamflow during 1967–2000. Annual fluctuations were the most representative signals in streamflow variability for the North River and West River over the period 1967–2010. Human activities including dam construction, land change and socioeconomic development posed increasing influences on hydrologic conditions in the JRB. Seasonal variability of streamflow and sediment discharge changed significantly between the two periods divided by the jumping point (1992), identified when dams were constructed extensively in the North River and West River. This research provided important insights into the hydrologic consequences of climate change and human activities in a subtropical coastal watershed of southeast China.     

基于RDI指数的云南1960~2013年#br# 旱涝变化特征分析

利用云南省40个气象站逐日降水量和蒸发量数据，采用RDI指数研究云南旱涝灾害的时空分布特征。结果表明：云南年际、季节旱涝与历史记录十分一致，1960~2013年云南年RDI指数呈下降趋势，表现为变干趋势，但不显著；2001年以前发生雨涝年的强度和站次比较干旱年明显，在此之后，发生干旱年的强度和站次比较雨涝年明显。季节尺度上，春季呈显著的变湿趋势，夏、秋、冬季呈不显著的变干趋势；春、夏季分别突变于1980年和1965年。从空间分布上来看，年、夏、秋、冬季整体以滇南和滇东北呈变干趋势，而滇西北呈变湿趋势；春季除滇东北外，其余区域均呈变湿趋势；年际、季节干旱频率以滇西北、滇西南、滇东南较高；年、春、夏、秋季重旱频率以滇中和滇东十分突出；年、夏、秋季特旱频率均以滇东北十分突出，春季滇中和滇东北极易发生特旱；冬季以滇中重旱频率较高，特旱极易发生在滇西北、滇西南、滇东北。年际、季节雨涝频率以滇西、滇东南较突出。年重、特涝频率以滇西南十分突出；春季重涝频率以滇西南和滇中较突出，特涝频率以滇中和滇东南较突出；夏季重、特涝频率均以滇西北较高；秋季重涝频率以滇西北较高，特涝频率以滇东南较高；冬季重涝频率以滇东南较突出，特涝频率以滇西北较高。 关键词： 云南省；RDI指数；旱涝变化趋势；时空特征     

三峡库区降水量的空间插值方法及时空分布

三峡库区是一个特殊的地理单元，分析库区降水的时空特征具有重要意义。利用三峡库区及周边46个气象站点资料，分别采用反距离加权法、样条函数法、普通克里金法、协同克里金法等4种空间插值方法，对三峡库区1961~2005年45年间的年平均降水量、月平均降水量进行了空间插值模拟与交叉检验，并对三峡库区降水量的时空分布特征进行了分析。检验结果表明，考虑高程的协同克里金法整体插值效果要优于其他3种插值法。但通过站点误差分析，协同克里金法并非对每一个站点的插值精度都高。研究发现，在剔除其中2个高海拔站点的情况下，可以显著提高协同克里金的空间插值效果。由插值得到的三峡库区降水分布图可知，大部分区域的年平均降水量处于 1000~1200 mm ，而年内降水分配不均匀，夏季降水约占年降水量的45%。     

Land cover changes as impacted by spatio-temporal rainfall variability along the Ethiopian Rift Valley escarpment

Magnitudes of land cover changes nowadays can be assessed properly, but their driving forces are subject to many discussions. Next to the accepted role of human influence, the impact of natural climate variability is often neglected. In this paper, the impact of rainfall variability on land cover changes (LCC) is investigated for the western escarpment of the Raya Graben along the northern Ethiopian Rift Valley. First, LCC between 2000 and 2014 were analysed at specific time steps using Landsat imagery. Based on the obtained LCC maps, the link was set with rainfall variability, obtained by means of the satellite-derived rainfall estimates (RFEs) from NOAA-CPC. After a correction by the incorporation of local meteorological station data, these estimates prove to be good estimators for the actual amount of precipitation (ρ _RFE1.0 = 0.85, p = 0.00, n = 126; ρ _RFE2.0 = 0.76, p = 0.00, n = 934). By performing several linear regression analyses, a significant positive relationship between the precipitation parameter DIFF 5Y (i.e. the at-RFE pixel scale difference in five-year average annual precipitation for the two periods preceding the land cover maps) and the changes in the woody vegetation cover was found (standardised regression coefficient β = 0.23, p = 0.02, n = 108). Despite the dominance of direct human impact, further greening of the study area can be expected for the future concomitantly to a wetter climate, if all other factors remain constant.     

210Pb deposition in the far East Asia: controlling factors of its spatial and temporal variations

In order to better understand the behavior of ²¹⁰Pb deposition in Far East Asia, comprehensive data of monthly ²¹⁰Pb deposition, which includes several time-series and spatial distribution data at 14 stations in Japan and 2 stations in Taiwan, were analyzed. Pb-210 deposition at most of the sites exhibited a typical seasonal change with higher values in winter and lower values in summer; especially, the greatest ²¹⁰Pb deposition in the world occurred in winter at sites beside the Japan Sea. The deposition behavior of ²¹⁰Pb in Far East Asia differed between winter and summer. The meteorological phenomenon peculiar to winter of the Japan Sea side, i.e., formation of the Japan Sea convergence zone, might cause the high ²¹⁰Pb concentration in rainwater, as may heavy snowfall. The ²¹⁰Pb concentration in rainwater showed long-term variability, although this differed between winter and summer. This long-term variability may be related to climatological factors such as El Niño.     

Both reindeer management and several other land use factors explain the reduction in ground lichens (Cladonia spp.) in pastures grazed by semi-domesticated reindeer in Finland

Roles of intensive reindeer grazing and several additional land use factors in the reduction in ground lichens (Cladonia spp.) in pastures grazed by the semi-domesticated reindeer have been argued in Finland. Our analysis showed that several factors and processes explain the standing biomass of lichens (during 2005–2008) and the recent changes in this biomass (after 1995–1996) on lichen pastures located in the 20 northernmost herding districts in Finland. The higher the long-term reindeer densities on the lichen pastures the lower was the lichen biomass. The lichen biomass was also strongly affected by the grazing system; the lowest biomass values of lichens were measured in all grazing areas that were used in the snow-free seasons. The lichen biomass in pine forests less than 80 years old and in all mountain type lichen pastures was lower than that in mature and old pine forests. The lichen biomass also decreased as the proportion of arboreal lichen pastures within a district decreased and the proportion of human infrastructure increased. The aerial drift of heavy metals from the Kola Peninsula appeared to reduce lichens in a small north-eastern part of the study area. Increases in summer precipitation and winter temperatures increased the amount of lichens, but increases in summer temperatures and winter precipitation had the opposite effect. Reindeer densities, grazing system, pasture type and the previous abiotic factors were also associated with the reduction in lichen biomass between the inventories. We conclude that several local, regional and even global factors and processes affect the state of reindeer pastures in large and complex grazing ecosystems. Therefore, more comprehensive research and management strategies for the entire reindeer herding environment are needed.     

基于Kriging插值的1961~2005年淮河流域降水时空演变特征分析

利用淮河流域4省170个气象站点1961~2005年的降水观测数据，采用Kriging法对淮河流域各季及年降水量进行了插值，得到了1 km×1 km降水栅格序列。在此基础上，对淮河流域降水的时空格局及其变化特征进行了分析。结果表明：淮河流域降水量的空间分布基本呈南高北低、山区多于平原、近海多于内陆的格局。近45 a来淮河流域降水量的年际波动较为强烈，而变化趋势不显著。流域内汛期和年降水量的年代际变化则具有明显的阶段性，主要表现在20世纪90年代前基本为下降趋势，2000年后明显上升。当前，淮河流域正处于降水的高气候变率时期。45 a来，降水的空间格局发生了一定的变化，表现在淮河中上游和干流沿岸地区的降水量升高，而流域东北部的降水则呈下降趋势