HYDROLOGIC BUDGET FOR A FRESHWATER MARSH IN FLORIDA1

ABSTRACT: Accurate water balance calculations are essential for water resource and environmental management decisions, but many of the terms used in the equation are difficult to measure. In this study, a method for measuring rates of evapotranspiration and net seepage from a freshwater marsh in southwest Florida is described. The results are compared to evaporation pan estimates as well as to calculations that balanced all the terms in the hydrologic budget. The measured rates of evapotranspiration showed a. distinct seasonal trend ranging from an average high of 0.24 in/d during July 1992 to a low of 0.06 in/d in January 1993. Evapotranspiration rates were higher than Class A evaporation pan measurements during July and August, indicating transpiration by plants exceeded evaporation by pans. Net ground water seepage flowed out of the marsh except during periods of high water table conditions. When all terms in the hydrologic budget were evaluated, the equation balanced on a yearly basis with an error of 2 percent, on a seasonal basis with errors less than 7 percent, but on a monthly basis errors were as great as 30 percent. Total annual rainfall on the marsh was 45 percent of the total marsh hydrologic input and was approximately equal to the loss by evapotranspiration of 41 percent.     

Revisiting the Thornthwaite and Mather Water Balance1

Abstract: This technical note clarifies confusion currently present in research using and/or citing the 1955 and 1957 editions of the Thornthwaite and Mather Water Balance (or Budget) resulting from corrections to errant tables in the 1955 edition made by the authors for the 1957 edition. Confusion over the two editions and the formulas used have clouded the results of research, management, and educational publications ever since, resulting in frequent misunderstanding of the method’s utility as well as how its results compare with other frequently used methods for estimating evapotranspiration.     

Sensitivity of Landsat‐Scale Energy Balance to Aerodynamic Variability in Mountains and Complex Terrain

The speed and direction of air flow through complex terrain are difficult to define. Both impact sensible and latent heat flux exchanges at the surface. Evapotranspiration (ET) models such as Mapping EvapoTranspiration at high Resolution with Internalized Calibration (METRIC?) estimate ET as a residual of the surface energy process and are thus sensitive to aerodynamics, including terrain‐induced impacts on roughness governing convective heat transfer (H). There is a need to explore the sensitivities of H estimation and thereby ET estimation to wind speed and terrain roughness in mountainous areas and to determine the merit of operating complex mesoscale wind field models in conjunction with the energy balance process. A sensitivity analysis is explored in METRIC where we increased wind speed in proportion to a relative elevation parameter and we increased aerodynamic roughness to assimilate impacts of relative terrain roughness, estimated in proportion to standard deviation of elevation within a 3 km locality. These aerodynamic modifications increased convective heat transfer in complex terrain and reduced estimated ET. In other sensitivity runs, we reduced estimated wind speed on estimated leeward slopes. Estimated ET with and without these sensitivity adjustments is shown for mountainous areas of Montana and Nevada. Changes in ET ranged from little change (<5%) for lower slopes to about 30% reductions on windward slopes and 25% increases on leeward slopes for some mid to high elevations in the Montana application.     

渭河流域植被WUE遥感估算及其时空特征

论文基于估算NPP的CASA模型和估算ET的三角形模型对水分限制因子算法进行改进的基础上,构建了由NPP子模型和ET子模型组成的WUE遥感估算模型,以2010年相关MODIS影像和气象参量为数据源,实现了渭河流域WUE的估算,并对WUE的时空特征及其与年内气温、降雨的关系进行了分析。研究表明：1）WUE模拟结果与通量观测数据以及生态系统模型模拟结果均具有一定的可比性,各模型模拟结果存在差异可能与WUE定义、模拟区域、使用数据源以及使用植被覆盖分类底图等存在差异有关;2）渭河流域WUE年内分布呈现微“双峰”型格局,以8月最高,春、夏、秋、冬四季WUE分别为0.57、1.05、0.66、0.12 gC·m^-2·mm^-1,呈现夏季>秋季>春季>冬季的特征;3）渭河流域WUE空间分布呈现子午岭、黄龙山、六盘山以及秦岭北坡等林区高,西安市建成区、子流域上游低植被覆盖区以及局部旱作农业区低的分异特征;4）渭河流域尺度上,WUE随年内气温和降雨的变化均呈现5阶段的变化特征,但变化形式存在差异。