Future Changes in Wet and Dry Season Characteristics in CMIP5 and CMIP6 simulations

Caroline M Wainwright,Emily Black,Richard P Allan

doi:10.1175/jhm-d-21-0017.1

Abstract

AbstractClimate change will result in more dry days and longer dry spells, however, the resulting impacts on crop growth depend on the timing of these longer dry spells in the annual cycle. Using an ensemble of Coupled Model Intercomparison Project Phase 5 and Phase 6 (CMIP5 and CMIP6) simulations, and a range of emission scenarios, here we examine changes in wet and dry spell characteristics under future climate change across the extended tropics in wet and dry seasons separately. Delays in the wet seasons by up to two weeks are projected by 2070-2099 across South America, Southern Africa, West Africa and the Sahel. An increase in both mean and maximum dry spell length during the dry season is found across Central and South America, Southern Africa and Australia, with a reduction in dry season rainfall also found in these regions. Mean dry season dry spell lengths increase by 5-10 days over north-east South America and south-west Africa. However, changes in dry spell length during the wet season are much smaller across the tropics with limited model consensus. Mean dry season maximum temperature increases are found to be up to 3°C higher than mean wet season maximum temperature increases over South America, Southern Africa and parts of Asia. Longer dry spells, fewer wet days, and higher temperatures during the dry season may lead to increasing dry season aridity, and have detrimental consequences for perennial crops.

Highlights

Climate change will result in more dry days and longer dry spells; this has the potential to lead to negative impacts on crop yields and food security, as water stress limits crop growth
Changes in the mean and maximum lengths of wet and dry spells have been calculated separately for the climatological wet and dry seasons using an ensemble of Coupled Model Intercomparison Project phase 5 (CMIP5) and Coupled Model Intercomparison Project phase 6 (CMIP6) models across the global tropics and subtropics
An objective methodology is used to classify the seasonality at each location and to determine the timing of the climatological wet and dry season(s); metrics including total seasonal rainfall, number of rainy days, rain per rainy day, and the mean and maximum length of wet and dry spells are calculated for the wet and dry seasons separately

Summary

Introduction

Climate change will result in more dry days and longer dry spells; this has the potential to lead to negative impacts on crop yields and food security, as water stress limits crop growth. A larger increase in precipitation intensity compared to mean precipitation is balanced by a decrease in the number of wet days, resulting in longer dry spells and shorter wet spells (Giorgi et al 2011; Seneviratne et al 2012; Sillmann et al 2013b). These longer dry spells may have negative impacts on crop yields and food production (Rockström et al 2010), as Denotes content that is immediately available upon publication as open access

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Conclusion