Simulating the impact of past and future land cover and climate change on the global hydrological system using PCR-GLOBWB

Abstract:

We investigate the influence of both human-induced land cover change and climate change in a series of experiments with a global hydrological model (PCR-GLOBWB 2.0, Sutanudjaja et al., 2014). First, we analyze the impact of land cover changes by applying the static land cover of 1850 and 2000 in two separate experiments that are otherwise subject to the same forcing (CRU-derived daily temperature, precipitation and reference potential evapotranspiration, 1979-2010). This land cover change alone, mainly due to expansion of crop and pasture, results in differences in annual mean discharge of over 1000 m³/s and over 10% in large areas of the world. Evapotranspiration changes reach 30 mm/month. Furthermore, for validation purposes we compare these results to an experiment that includes human effects such as irrigation and reservoirs, as well as to a default experiment with a slightly different land cover parameterization.

To investigate the influence of both land cover and climate change over time, we perform longer experiments applying input from the EC-Earth and CESM GCMs to PCR-GLOBWB. This allows us to extend the experiments from 1850 to 2100. We use two greenhouse gas emission scenarios for the 21st century: RCP2.6, a low-end scenario, as well as the high-end RCP8.5 scenario. Daily precipitation, temperature and reference potential evapotranspiration are bias-corrected using the ISI-MIP method (Hempel et al., 2013). First, land cover is fixed at 1850 and PCR-GLOBWB only experiences climate change from 1850 to 2100. Then, land cover is varied according to the historical reconstructions and future projections per RCP (Hurtt et al., 2011). Anthropogenic effects are excluded, so differences between these experiments are only due to land cover change. We analyze changes in discharge over catchment areas as well as evapotranspiration on cell basis. This is the first study with PCR-GLOBWB to evaluate the impact of both climate and land cover change over time for both past and future.