Estimates of spatial variation in evaporation using satellite-derived surface temperature and a water balance model

Evaporation dominates the water balance in and and semi-arid areas. The estimation of evaporation by land-cover type is important for proper management of scarce water resources. Here, we present a method to assess spatial and temporal patterns of actual evaporation by relating water balance evaporation estimates to satellite-derived radiometric surface temperature. The method is applied to a heterogeneous landscape in the Krishna River basin in south India using 10-day composites of NOAA advanced very high-resolution radiometer satellite imagery. The surface temperature predicts the difference between reference evaporation and modelled actual evaporation well in the four catchments (r(2) = 0.85 to r(2) = 0.88). Spatial and temporal variations in evaporation are linked to vegetation type and irrigation. During the monsoon season (June-September), evaporation occurs quite uniformly over the case-study area (1.7-2.1 mm day(-1)), since precipitation is in excess of soil moisture holding capacity, but it is higher in irrigated areas (2.2-2.7 unit day(-1)). In the post-monsoon season (December-March) evaporation is highest in irrigated areas (2.4 mm day(-1)). A seemingly reasonable estimate of temporal and spatial patterns of evaporation can be made without the use of more complex and data-intensive methods; the method also constrains satellite estimates of evaporation by the annual water balance, thereby assuring accuracy at the seasonal and annual time-scales. Copyright (c) 2007 John Wiley & Sons, Ltd.