Meteorological drought is generally regarded as the cause of other types of droughts. This study firstly analyzed the characteristics of meteorological drought and hydrological drought in different climate regions all over the world during a long time period (1902–2014); then, the maximum Pearson correlation coefficients (MPCC) of meteorological drought and hydrological drought at different time scales were calculated to determine the drought response time (DRT) in each climate region. The results revealed that: 1) meteorological drought in most climate regions intensified during 1902–1958 but showed a wetting trend during 1959–2014. Compared with the characteristics of meteorological drought, the change of hydrological drought was slightly different. Hydrological drought weakened during 1902–1958 but intensified slightly during 1959–2014; however, the magnitude of the changing rate was relatively small. 2) The drought response relationship in the Cf (i.e., continental wet warm) climate region was the strongest, and that in the E (i.e., polar) climate region was the weakest. 3) Globally, the DRTs in various climate regions were mainly 5–10 months, which were mainly related to the climate type. The outcomes of this study can provide a reference for further revealing the propagation mechanism from meteorological drought to hydrological drought in different climate regions.

Climate change is expected to have a significant impact on water security, with higher temperatures causing both enhanced droughts and flood extremes. Here, using global flow data from non-urban catchments, we investigate the sensitivity of flood volume to changes in concurrent surface air temperature. We find most of the world shows decreases in flood volumes with increasing temperature. To understand why this correlation exists, we assess the sensitivity of the above result to mean daily temperatures (climate region), catchment size, and severity of the flood event. Our results indicate that most of the world shows decreases in flood volume with rising temperature for frequent events (50th percentile in this study) and a lesser decrease for rarer events. Changes in the flood volume in tropical regions show the greatest sensitivity to flood percentiles and catchment size. Large catchments in the tropics (≥ 1000 km2) have considerable sensitivities of flood volume with temperature at rates of -10 to -5%/ °C for frequent events (< 90th percentile) whereas small catchments (1000 km2) have sensitivities that only -5%/ °C or greater (i.e., less magnitude). On the other hand, when temperature increases, smaller catchments in the regions are likely to be exposed to more severe flooding at rates up to 15%/ °C for the most severe floods (99.99 percentile in this study) while the rate for large catchments approach zero. Although this study does not seek to find a causality between air temperature and flood runoff, the results suggest a possible decrease in water security with climate change, particularly in large tropical catchments.