Abstract
The Paris agreement was adopted to hold the global average temperature increase to well below 2 °C and pursue efforts to limit it to 1.5 °C. Here, we investigate the event-to-event hydroclimatic intensity, where an event is a pair of adjacent wet and dry spells, under future warming scenarios. According to a set of targeted multi-model large ensemble experiments, event-wise intensification will significantly increase globally for an additional 0.5 °C warming beyond 1.5 °C. In high latitudinal regions of the North American continent and Eurasia, this intensification is likely to involve overwhelming increases in wet spell intensity. Western and Eastern North America will likely experience more intense wet spells with negligible changes of dry spells. For the Mediterranean region, enhancement of dry spells seems to be dominating compared to the decrease in wet spell strength, and this will lead to an overall event-wise intensification. Furthermore, the extreme intensification could be 10 times stronger than the mean intensification. The high damage potential of such drastic changes between flood and drought conditions poses a major challenge to adaptation, and the findings suggest that risks could be substantially reduced by achieving a 1.5 °C target.
Highlights
Human-induced global warming has contributed to an increase in the magnitude and frequency of climate extremes[11]
Inspired by an earlier work[16], here, we propose the “event-to-event hydrological intensification index” (E2E), which combines normalized “aggregated precipitation intensity” (API) and “dry spell length” (DSL), to capture the interconnectivity of adjacent dry and wet spells and the intensification of their phase shifts
The number of events increased with shorter wet spells and extended dry spells, and both the intensity (DSL) and frequency terms contributed to the increase in total dry days
Summary
We calculate the dry spell length (DSL) as the consecutive number of dry days and the total daily precipitation during the wet spell, which is called the “aggregated precipitation intensity” (API) throughout this study. For the analysis of the extreme cases of hydroclimatic intensity, the 99th percentile (P99) of E2E was obtained along with the DSL and API components of that event This resulted in 100 values for each parameter (i.e., P99 of E2E, etc.) per model per experiment (ALL, 1.5 °C, and 2 °C). If the total precipitation (P) can be represented as a combination of the mean precipitation intensity (I, that is the mean API for wet spells) and mean frequency (n), i.e., as P = n.I, change in the total precipitation from 1.5 °C to 2 °C warming can be decomposed as follows: ΔP = P′–P = (n + Δn). Assessment of the statistical significance of probability density functions were conducted using two-sided Kolmogorov-Smirnov test
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