Joint extremes of precipitation and temperature in Europe: seasonal trends and patterns

<p>Co-occurring extremes of multiple climate variables can cause disproportionate damage to human activities and ecosystems. Their impacts may be larger than the combination of those caused by individual extremes. Moreover, associated risks may be compounded by dependence structures between climate variables, which enhance the frequency of joint extremes beyond the level that would be observed if variables were independent. Joint extremes of precipitation (P) and temperature (T) are of particular interest as they can simultaneously affect water resources, ecosystems, and agricultural and energy systems, all of which are closely interconnected.</p><p>We analyse non-parametric trends and spatial patterns in the occurrences of joint extremes of P and T in Europe using observational E-OBS daily data at 0.1&#176; spatial resolution from 1950 to 2019. For each grid-cell and calendar month, we define low (high) extremes as values smaller (larger) than quantiles of empirical frequency distributions. These are obtained from times series smoothed using backward moving averages. Time averaging is used to detect extremes at &#160;time scales relevant for the variable and type of hazard considered, e.g. we use longer windows for low precipitation extremes to represent reduced freshwater availability. We compute statistically significant trends in occurrence and spatial extent of both joint and univariate extremes, and investigate their correlations with analogous trends in P and T time series. Several quantile thresholds and different combinations of averaging window duration are used to evaluate the sensitivity of the results. The analysis is repeated on two sub-periods (1950-1984 and 1985-2019) to investigate whether there is a change in the strength of signals over time. Special attention is given to regions experiencing extended periods with zero precipitation, such as the Mediterranean, and regions with a seasonal snow climate, such as in the Alps and Northern Europe.</p><p>&#160;</p><p><em>Acknowledgement: This work is funded by the Strategic Research Initiative &#8220;Land Atmosphere Interactions in Cold Environments&#8221; (LATICE) of the University of Oslo (project number: UiO/GEO103920).</em></p>