Identifying a transition climate zone in an arid river basin using the evaporative stress index

Abstract

Aridity indices have been widely used in climate classification. However, there is not enough evidence fortheir ability in identifying the multiple climate types in areas with complex topography and landscape, especially in thoseareas with a transition climate. This study compares a traditional meteorological aridity index (AI), defined as the ratioof precipitation (P) to potential evapotranspiration (PET), with a hydrological aridity index, the evaporative stress index(ESI) defined as the ratio of actual evapotranspiration (AET) to PET in the Heihe River Basin (HRB) of arid northwesternChina. PET was estimated using the Penman–Monteith and Hamon methods. The aridity indices were calculated usingthe high-resolution climate data simulated with a regional climate model for the period of 1980–2010. The climate classifiedby AI shows a climate type for the upper basin and a second type for the middle and lower basin, while three differentclimate types are found using ESI, each for one river basin, indicating that only ESI is able to identify a transition climatezone in the middle basin. The difference between the two indices is also seen in the interannual variability and extremedry/wet events. The magnitude of variability in the middle basin is close to that in the lower basin for AI, but differentfor ESI. AI had a larger magnitude of the relative interannual variability and a greater decreasing rate from 1980 to 2010than ESI, suggesting the role of local hydrological processes in moderating extreme climate events. Thus, the hydrologicalaridity index is better than the meteorological aridity index for climate classification in the arid Heihe River Basin.

Citation

Liu, Yongqiang; Hao, Lu; Zhou, Decheng; Pan, Cen; Liu, Peilong; Xiong, Zhe; Sun, Ge. 2019. Identifying a transition climate zone in an arid river basin using the evaporative stress index. Natural Hazards and Earth System Sciences. 19(10): 2281-2294. https://doi.org/10.5194/nhess-19-2281-2019.