DOI: 10.48364/isimip.982724.1
title: ISIMIP3a atmospheric climate input data

description: The Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) provides a framework for the collation of a consistent set of climate impact data across sectors and scales. It also provides a unique opportunity for considering interactions between climate change impacts across sectors through consistent scenarios.<br>The ISIMIP3a part of the third simulation round is dedicated to i) impact model evaluation and improvement and ii) detection and attribution of observed impacts according to the framework of IPCC Working Group II AR5 Chapter 18 and AR6 chapter 16. To this end all simulations are driven by observed socio-economic information combined with either observed (factual) climate data or a detrended (counterfactual) version of the observed climate allowing for the generation of a "no climate change" impact baseline.<br>We provide four factual climate input datasets for ISIMIP3a: GSWP3-W5E5, 20CRv3-W5E5, 20CRv3-ERA5, and 20CRv3. All of them have daily temporal and 0.5° spatial resolution. Their temporal coverage varies, with GSWP3-W5E5 and 20CRv3-W5E5 covering 1901-2019, while 20CRv3-ERA5 and 20CRv3 cover 1901-2021 and 1901-2015, respectively. For every factual dataset (obsclim) we provide an associated counterfactual dataset (counterclim) covering the same time period, 100 years worth of climate data to be used for model spin-up (spinclim), and 50 years worth of climate data for the transition from spinclim to counterclim or obsclim (transclim).<br>Version 1.1 fixes missing values in GSWP3-W5E5 snow fall input data (see https://data.isimip.org/caveats/26/).
description: The transclim data are identical to the last 50 years of the associated spinclim data. The spinclim data are identical to the first 100 years of the associated counterclim data. The counterclim data are a detrended version of the associated obsclim data, where the detrending is done using version 1.1 of the ATTRICI method (Mengel et al. 2021). In the following we briefly describe the obsclim datasets:<br>The GSWP3-W5E5 dataset is based on GSWP3 v1.09 (Kim 2017) and W5E5 v2.0 (Cucchi et al. 2020, Lange et al. 2021). The GSWP3 dataset is a dynamically downscaled and bias-adjusted version of the Twentieth Century Reanalysis version 2 (20CRv2; Compo et al. 2011). The W5E5 dataset is a bias-adjusted version of the latest version of the European Reanalysis (ERA5; Hersbach et al. 2020). For GSWP3-W5E5, we combine W5E5 for the time period 1979-2019 with GSWP3 bias-adjusted towards W5E5 for the time period 1901-1978. The bias adjustment is done using ISIMIP3BASD v2.5.1 (Lange 2019, 2021) in order to reduce discontinuities at the 1978/1979 transition. For more details see Mengel et al. (2021).<br>The 20CRv3-W5E5 dataset is based on W5E5 v2.0 and ensemble member 1 of the Twentieth Century Reanalysis version 3 (20CRv3; Slivinski et al. 2019, 2021) interpolated to 0.5° spatial resolution. For 20CRv3-W5E5, we combine W5E5 for the time period 1979-2019 with 20CRv3 bias-adjusted (using ISIMIP3BASD v2.5.1) towards W5E5 for the time period 1901-1978.<br>The 20CRv3-ERA5 dataset is created in the same way as 20CRv3-W5E5, but using ERA5 instead of W5E5 for the time period 1979-2021, and also as the bias adjustment target for the time period 1901-1978.<br>The 20CRv3 dataset is ensemble member 1 of 20CRv3 interpolated to 0.5° spatial resolution but not bias-adjusted to any other dataset.