Dependence of 3-month Standardized Precipitation-Evapotranspiration Index dryness/wetness sensitivity on climatological precipitation over southwest China

In this study, we estimated the respective contributions of precipitation and reference evapotranspiration (ET0) to annual SPEI-3 (3-month Standardized Precipitation-Evapotranspiration Index) anomalies over southwest China (SWC) using numerical experiments. Results show that the dominant factor (i.e., precipitation or ET0) for the dryness/wetness anomalies during 1961-2012 existed due to inter-annual and inter-decadal changes over SWC, which indicates the underlying mechanisms of dry/wet conditions have changed. On the other hand, we calculate the dryness/wetness sensitivity to precipitation or ET0 (defined as changes in SPEI-3 per millimetre) and find that the dryness/wetness sensitivity to ET0 is higher than that to precipitation for the whole SWC and the overwhelming majority (99%) of the 269 sites. Overall, the above findings imply that the role of ET0 in the dry/wet condition evolution is vital and should be paid more attentions. For the magnitude of the dryness/wetness sensitivity to precipitation or ET0, an evident increase from the southeast to northwest SWC is identified. Based on the analyses of the relationship between dryness/wetness sensitivity and climatological condition (i.e., precipitation, ET0, and aridity), the sensitivity magnitude is dependent on climatological precipitation and generally decreases with its increase. This study provides a wealth of quantitative information (e.g., dryness/wetness anomalies [sensitivity] caused by [to] precipitation and ET0) for better understanding the underlying mechanisms of the dry/wet condition evolution.