Response of mean annual evapotranspiration to vegetation changes at catchment scale

TLDR

Forested catchments exhibit higher evapotranspiration than grassed ones, and land‑use changes influence water balance through factors such as rainfall interception, radiation, advection, turbulence, leaf area, and plant‑available water capacity, whose relative importance varies with climate, soil, and vegetation. A simple two‑parameter model was developed that links mean annual evapotranspiration to rainfall, potential evapotranspiration, and plant‑available water capacity, based on observations and prior theory. The model, which predicts mean annual evapotranspiration from rainfall, potential evapotranspiration, and plant‑available water capacity, achieved a mean absolute error of 42 mm (6 %) with a slope of 1.00 and correlation of 0.96, and demonstrates utility for water‑yield and recharge modeling and for evaluating long‑term vegetation impacts.

Abstract

It is now well established that forested catchments have higher evapotranspiration than grassed catchments. Thus land use management and rehabilitation strategies will have an impact on catchment water balance and hence water yield and groundwater recharge. The key controls on evapotranspiration are rainfall interception, net radiation, advection, turbulent transport, leaf area, and plant‐available water capacity. The relative importance of these factors depends on climate, soil, and vegetation conditions. Results from over 250 catchments worldwide show that for a given forest cover, there is a good relationship between long‐term average evapotranspiration and rainfall. From these observations and on the basis of previous theoretical work a simple two‐parameter model was developed that relates mean annual evapotranspiration to rainfall, potential evapotranspiration, and plant‐available water capacity. The mean absolute error between modeled and measured evapotranspiration was 42 mm or 6.0%; the least squares line through the origin had as lope of 1.00 and a correlation coefficient of 0.96. The model showed potential for a variety of applications including water yield modeling and recharge estimation. The model is a practical tool that can be readily used for assessing the long‐term average effect of vegetation changes on catchment evapotranspiration and is scientifically justifiable.