Using the aridity index to assess recent climate change: a case study of the Lancang River Basin, China

Abstract

As one of the most important climatic variables, annual evapotranspiration (E) reflects the complex interactions between atmosphere, vegetation, soil and hydrological process at global and regional scales. It is largely determined by potential evapotranspiration (E0) and precipitation (P). Aridity index (E0/P) which can be defined as the ratio of annual potential evapotranspiration to annual precipitation, can be used to represent annual evapotranspiration. As result it has become an important indicator to assess water-related climate change. This study utilizes the aridity index to reveal the recent climate change patterns in the Lancang River Basin, China. A new non parametric estimator of climate elasticity has also been developed. Using the daily meteorological records (1961–2005) of precipitation, air temperature, wind speed, relative humidity and sunshine hours from 35 stations, changes in spatial and temporal characteristics of P, E0, E, and E0/P are analyzed. The results reveal some important new findings, which can be summarized as: (a) new findings show that the spatial distribution of, and the correlation coefficients between P, E0, E, and E0/P possess strong latitude zonality; (b) high consistency in the temporal variation of P and E has been detected. The main periodicity of the E and E0/P series varies greatly for the three sub basins, and an anti-phase relationship between them has also been found; (c) our newly developed nonparametric estimator of climate elasticity can be successfully used in assessing the sensitivity of climate system. Climate elasticity of E in relation to E0 and P increases for most of the regions in the study area, suggesting that E becomes more sensitive to changes in the corresponding climatic variable during the study period. The study demonstrates the importance of the aridity index in the water-related climate change studies which has been neglected for a long time by most hydrologists and managers.