Assessing climate change induced modification of Penman potential evaporation and runoff sensitivity in a large water-limited basin

Abstract

Potential evaporation (Ep) reflects the combined effects of four key meteorological variables: (i) net radiation (Rn); (ii) wind speed (u); (iii) relative humidity (rh); and (iv) air temperature (Ta). Here, attribution analysis was conducted to investigate the contribution of the four key meteorological variables to changes of a physically-based Ep in a large water-limited basin, the Yellow River Basin (YRB), China. Then the influences of these changes, and precipitation (P) changes, on streamflow (Q) were explored analytically. Results show that: (i) Ep presented different temporal trends for the water yielding region (WYR) and water consuming region (WCR) with a overall changes of +0.16 mm a−2 and −0.66 mm a−2 during 1961–2010, respectively; (ii) trend analysis of Ep and the four key meteorological variables at the basin scale showed that increasing trend in Ta increased Ep during 1961–2010, while changes in Rn and u increased the 1961–1979 Ep rate and reduced it during 1980–1994 and 1995–2010; (iii) revealed by attribution analysis, Ep increased by changes in Ta and rh and reduced by changes of Rn and u in both WYR and WCR, in all, Ep rate presented positive and negative trends in the WYR and WCR, respectively; (iv) the changes of Q and actual evaporation (E) are much more sensitive to changes in P than the changes in Ep; and (v) of critical importance for water resource management of the YRB changes in Q are mainly attributed to changes in catchment-specific parameter (n) and P, while Ep reduced Q in WYR and increased Q in WCR. These results indicated that the causes of trend of Ep rates, influenced by combined effects of radiative and aerodynamic variables should be explicitly explained using fully physically based Ep formulations. Additionally, in the water-limited YRB, changes of Q are primarily controlled by the changes in catchment conditions, and secondarily by hydroclimatic factors where the available water (P) rather than energy condition (Ep) is more important. Better understanding all of these relationships and how they have varied will help water resource management in a changing climate.