A framework for ensemble modelling of climate change impacts on lakes worldwide: the ISIMIP Lake Sector

Abstract

Abstract. Empirical evidence demonstrates that lakes and reservoirs are warming across the globe. Consequently, there is an increased need to project future changes in lake thermal structure and resulting changes in lake biogeochemistry in order to plan for the likely impacts. Previous studies of the impacts of climate change on lakes have often relied on a single model forced with limited scenario-driven projections of future climate for a relatively small number of lakes. As a result, our understanding of the effects of climate change on lakes is fragmentary, based on scattered studies using different data sources and modelling protocols, and mainly focused on individual lakes or lake regions. This has precluded identification of the main impacts of climate change on lakes at global and regional scales and has likely contributed to the lack of lake water quality considerations in policy-relevant documents, such as the Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC). Here, we describe a simulation protocol developed by the Lake Sector of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) for simulating climate change impacts on lakes using an ensemble of lake models and climate change scenarios for ISIMIP phases 2 and 3. The protocol prescribes lake simulations driven by climate forcing from gridded observations and different Earth system models under various representative greenhouse gas concentration pathways (RCPs), all consistently bias-corrected on a 0.5∘ × 0.5∘ global grid. In ISIMIP phase 2, 11 lake models were forced with these data to project the thermal structure of 62 well-studied lakes where data were available for calibration under historical conditions, and using uncalibrated models for 17 500 lakes defined for all global grid cells containing lakes. In ISIMIP phase 3, this approach was expanded to consider more lakes, more models, and more processes. The ISIMIP Lake Sector is the largest international effort to project future water temperature, thermal structure, and ice phenology of lakes at local and global scales and paves the way for future simulations of the impacts of climate change on water quality and biogeochemistry in lakes.

Global increase in methane production under future warming of lake bottom waters

“…Lake temperatures used in this study were simulated using two lake models, GOTM and SimStrat, which contributed to the ISIMIP2b lake sector (Golub et al, 2022). Specifically, the ISIMIP2b global lake simulations utilized GOTM v5.3 and SimStrat v1.4 with an added lake ice and snow module; SimStrat‐UoG (detailed model descriptions in Golub et al, 2022). The two models have been tested extensively in past studies including detailed validations across a spectrum of lake contexts.…”

“…Following the ISIMIP2b global lake sector protocol, each of these lake models were used to simulate lake temperatures at a 0.5°‐by‐0.5° grid resolution (Golub et al, 2022). For each 0.5° grid, the 1D models simulated daily temperature profiles in a cylindrical lake with the mean depth and surface area corresponding to the average of all known lakes within the grid.…”

“…Following the ISIMIP2b global lake sector protocol, each of these lake models were used to simulate lake temperatures at a 0.5°-by-0.5° grid resolution (Golub et al, 2022). For each 0.5° grid, NE/T011246/1; Svenska Forskningsrådet Formas, Grant/Award Number: 2018-01794 and2020-01091;Vetenskapsrådet, Grant/Award Number: 2016-04829, 2017-04405, 2018-04524, 2020-03222 and 2020DkIT Research Office; Irish Higher Education Authority: Landscape Funding; Spanish Agencia Estatal de Investigación; European Space Agency lakes experiencing an increase of up to 17 times the historical global average under RCP 8.5.…”

The pace of shifting seasons in lakes

“…An in-depth explanation of the ISIMIP Lake Sector is given by ref. 33. All ISIMIP Lake Sector projections investigated in this study were simulated via a lake model (see below) driven by an ensemble of bias-corrected climate projections, namely GFDL-ESM2M, HadGEM2-ES, IPSL-CM5A-LR, and MIROC5.…”

“…To investigate future (2021-2099) changes in the pace of the shifting seasons, modelled lake surface temperatures from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) phase 2b Lake Sector is analysed. These data include surface water temperature simulations from ~17,000 representative lakes worldwide as well as from 50 lakes with detailed bathymetry and observational validation data 33 . The ISIMIP projections are based on an ensemble of lake models, each forced with climate data from an ensemble of 20th and 21st century climate projections, under different anthropogenic greenhouse gas emission scenarios (Representative Concentration Pathway, RCP): RCP 2.6 (lowemission scenario), 6.0 (medium-high-emission), and 8.5 (high-emission), as well as a climate influenced solely by natural processes with no anthropogenic influence, defined according to a pre-industrial control simulation.…”