Downscaling probability of long heatwaves based on seasonal mean daily maximum temperatures

Abstract

Abstract. A methodology for estimating and downscaling the probability associated with the duration of heatwaves is presented and applied as a case study for Indian wheat crops. These probability estimates make use of empirical-statistical downscaling and statistical modelling of probability of occurrence and streak length statistics, and we present projections based on large multi-model ensembles of global climate models from the Coupled Model Intercomparison Project Phase 5 and three different emissions scenarios: Representative Concentration Pathways (RCPs) 2.6, 4.5, and 8.5. Our objective was to estimate the probabilities for heatwaves with more than 5 consecutive days with daily maximum temperature above 35 ∘C, which represent a condition that limits wheat yields. Such heatwaves are already quite frequent under current climate conditions, and downscaled estimates of the probability of occurrence in 2010 is in the range of 20 %–84 % depending on the location. For the year 2100, the high-emission scenario RCP8.5 suggests more frequent occurrences, with a probability in the range of 36 %–88 %. Our results also point to increased probabilities for a hot day to turn into a heatwave lasting more than 5 days, from roughly 8 %–20 % at present to 9 %–23 % in 2100 assuming future emissions according to the RCP8.5 scenario; however, these estimates were to a greater extent subject to systematic biases. We also demonstrate a downscaling methodology based on principal component analysis that can produce reasonable results even when the data are sparse with variable quality.

Comparison of statistical downscaling methods for climate change impact analysis on precipitation-driven drought

“…Our results suggest wetter winters and drier summers for Belgium, consistent with the results obtained from the CMIP5 GCMs (Tabari et al, 2015). An increase in the length of extreme dry spells (Breinl et al, 2020) and in aridity conditions (Tabari, 2020) was also found for western Europe. The same methodology is followed to assess the significance of the results after downscaling.…”

“…The most important indicators for this study are related to dry days, dry spells and total precipitation. A typical threshold used for separating wet and dry days is 0.1 mm (Pérez-Sánchez et al, 2018;Breinl et al, 2020). This value corresponds to the standard resolution used for precipitation observations.…”

“…Based on observations of more than 5000 rain gauges in the past 6 decades, Breinl et al (2020) assessed the historical evolution of dry spells in the USA, Europe and Australia. Both trends towards shorter and longer dry spells were found, depending on the location.…”

A Norwegian Approach to Downscaling

“…A reason for this step was that it adds a layer of quality control, and in retrospect, this technique is both elegant and a superior way of dealing with predictors, compared to traditional PP (Benestad, 2001). Time and time again, it has demonstrated merit (Benestad et al, 2002;Benestad, 2004;Benestad et al, 2005;Isaksen et al, 2007;Etzelmüller et al, 2011;Benestad, 2011;Førland et al, 2011;Hansen et al, 2014;Benestad and Mezghani, 2015;Benestad et al, 2015a;Mtongori et al, 2016;Benestad et al, 2016;Mezghani et al, 2017;Benestad et al, 2018;Mezghani et al, 2019;Parding et al, 2019;Erlandsen et al, 2020). In spite of the success with utilising common EOFs, a Google scholar search on '"common EOFs" downscaling' only had 63 hits (of which about 40 referred to our own work), despite more than 20 years since they first were introduced in ESD and the widespread need for climate change adaptation and downscaled results.…”

“…Contrary to common perceptions (Solomon et al, 2007, 11.10.1.3), ESD based on the climate approach is suitable for making inferences about extremes, and probably more so than RCMs. In addition to downscaling the probability of heavy rainfall, as presented above, we have proposed ways of downscaling pdfs to study how the duration and frequency of heatwaves is affected by climate change (Benestad et al, 2018). This strategy is inspired by dialogues with statisticians, and is based on https://doi.org/10.5194/gmd-2021-176 Preprint.…”