DOI: 10.48364/isimip.865475
title: DDM30 river routing network for ISIMIP3

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 AR5 Working Group II Chapter 18. 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" baseline.<br>The ISIMIP3b part of the third simulation round is dedicated to a quantification of climate-related risks at different levels of global warming and socio-economic change. ISIMIP3b group I simulations are based on historical climate change as simulated in CMIP6 combined with observed historical socio-economic forcing. ISIMIP3b group II simulations are based on climate change according to the CMIP6 future projections combined with socio-economic forcings fixed at 2015 levels. ISIMIP3b group III simulations additionally account for future changes in socio-economic forcing.<br>This dataset contains the river routing network input for ISIMIP3 simulations: DDM30 is a raster map which describes the drainage directions of surface water with a spatial resolution of 30’ longitude by 30’ latitude, and covers the land surface of the globe (without Antarctica). In addition to the routing network, DDM30 includes raster maps for basin numbers and slopes. More information can be found on the ISIMIP Homepage: https://www.isimip.org/gettingstarted/input-data-bias-adjustment/details/20/.
description: The routing network is provided to the water models (mainly from the ISIMIP global water sector) to route the simulated runoff to the ocean outlets or inland sinks. The data basis is the so-called DDM30 (Döll and Lehner, 2002) who generated a global 0.5° x 0.5° drainage direction map plus additional information as basin number and slopes. However, the DDM30 was designed for a land-ocean mask with 66896 grid cells which differs from the CRU land-ocean mask used within ISIMIP. Both land-ocean masks differ from each other mainly in coastal regions but also for several small islands that are dominantly appearing in the CRU land-ocean mask. <br>In the framework of the first model intercomparison project (Haddeland et al., 2011), the DDM30 was remapped to the CRU land-ocean mask. The new appearing grid cells were indicated by a “9” in the flow direction, a constant slope and a basin number. <br>However, the special treating of the new cells has resulted in unexpected side-effects, i.e. some modelling groups excluded those cells in their simulations. During the adaptation of the WaterGAP model for ISIMIP3, all “9” values were assigned to “0” (outflow to the Oceans) as those cells are exclusively located at the coasts.<br>Furthermore, it can be of interest for some assessments (Wang et al., 2018) to differentiate between inland sinks and cells draining to the Oceans (both originally assigned to “0”). Therefore, inland sinks are now indicated with a "-1". This information is available from the WaterGAP model.