Spatiotemporal trends of dryness/wetness duration and severity: The respective contribution of precipitation and temperature

This study explores the respective contributions of precipitation and temperature variability to the trends of the duration and severity of the dryness/wetness, and takes the Pearl River basin (PRB) in the southern China as a study example. The Standardized Precipitation Evapotranspiration Index (SPEI), which uses the monthly precipitation and temperature as input variables, was calculated based on the monthly precipitation and temperature records of 42 meteorological gauges during 1960–2015 in the PRB. The run theory was then applied to extract the dryness/wetness characteristics including the drought duration and severity and the wetting duration and severity. In addition, a simple algorithm for quantifying the respective contribution of the precipitation and temperature variability to the dryness/wetness trends was proposed; the algorithm determines the changes in the slope's magnitude (linear regression) for the dryness/wetness characteristics that were identified from different SPEI scenarios (i.e. the precipitation and temperature groups of observed, one of them detrended, and both detrended) using the run theory method. Our results showed that the increasing trends of drought duration and severity were more apparent in the northwestern areas with high elevation (>1000 m) than the southeastern areas with low elevation (<500 m), whereas the change trends of the wetness duration and severity exhibited opposite results. The variability of the precipitation and temperature played different roles in the trends of the dryness/wetness characteristics; the effects of the temperature changes on these trends were larger than the effects of the precipitation changes, i.e., an increase in the temperature clearly affected the change trends of duration and severity for the dryness/wetness. In the PRB, a slight increase in the average precipitation resulted in decreases in the trends of drought duration and severity of 9.89% and 19.63% respectively and increases in the trends of wetting duration and severity of 1.59% and 11.52%. However, a marked increase in the average temperature resulted in increases in the trends of drought duration, drought severity, wetting duration, and wetting severity of 48.38%, 55.16%, 46.21%, and 34.40%, respectively. Thus, in light of global warming, the government should focus more attention on the evolution of the dryness/wetness characteristics because increases in severe drought occurrences and flood severities and secondary disasters may result in more severe losses.