Impact model: H08

Sector: Water (global)
Region: global

H08 is a grid-cell based global hydrological model. It consists of six sub-models, namely land surface hydrology, river routing, reservoir operation, crop growth, environmental flow, and water abstraction. The formulations of sub-models are described in detail in Hanasaki et al. (2008a,b, 2010). In the standard simulation settings, H08 spatially covers the whole globe at a resolution of 0.5°×0.5° in order to assess geographical heterogeneity of hydrology and water use. Simulation period is typically for several decades and calculation interval is a day. The six sub-models exchange water fluxes and updates water storage at each calculation interval with the complete closure of water balance (the error is less than 0.01% of the total input precipitation). These characteristics enable us to explicitly simulate the major interaction between natural water cycle and major human activities of the globe. Source code and the manuals of H08 is open to public, available at http://h08.nies.go.jp.

In 2016, the water abstraction schemes of H08 has been substantially enhanced. In addition, a simple groundwater scheme was added to the land surface hydrology sub-model. It enabled us to estimate water abstraction from six major water sources, namely, streamflow regulated by global reservoirs (i.e. reservoirs regulating the flow of main channel of the world major rivers), aqueduct water transfer, local reservoirs, seawater desalination, renewable groundwater, and non-renewable groundwater. A model description paper is available at https://www.hydrol-earth-syst-sci.net/22/789/2018/.

H08 is one of the 13 global hydrology models following the ISIMIP2a protocol which form the base of simulations for the ISIMIP2a global water sector outputs; for a full technical description of the ISIMIP2a Simulation Data from Water (global) Sector, see this DOI link: http://doi.org/10.5880/PIK.2017.010

For ISIMIP2b, the new H08 (Hanasaki et al., 2018) was used. The model is substantially different from “classic H08” (Hanasaki et al. 2008a, 2008b, 2010) by mainly six points.
- Groundwater scheme was added.
- Groundwater abstraction scheme was added.
- Aqueduct water transfer scheme was added
- Scheme for return flow and delivery loss was added
- Reservoir scheme was updated
- Seawater desalination scheme was added

For ISIMIP3a/3b, the hydrological parameters of H08 have been tuned based on the study of Yoshida et al. (2022; https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021WR030660 ). We believe now the overall water balance is better estimated compared to previous versions. Due to some technical reasons, the parameters for subarctic climate (Dc) vary by longitudinal sections. This may cause sudden jumps in hydrological variables (e.g. soil moisture) at the borders of sections. See Yoshida et al. (2022) for further details. The tuned parameters include soil depth, which requires special attention in analyzing H08 simulation results. The soil in the H08 global hydrologic model has long been configured as a uniform single layer of 1 m (Hanasaki et al. 2008). In ISIMIP Phase 3, that configuration was changed by adopting the climate zone-specific parameter optimization presented in Yoshida et al. (2022). Now, H08 has climate-zone-specific soil depth and maximum soil moisture holding capacity. These spatial distributions are shown in SoilDepth.nc and SoilMoisMax.nc. There are two caveats here. First, there is still only one soil layer in H08. Second, as mentioned above, based on the discussion in Yoshida et al. (2022), the climatic classification of Dc (subarctic) was further separated into six subregions. Because they are separated by meridians (e.g., 60°E or 90°E), the distribution of soil moisture and water fluxes at high latitudes in the Northern Hemisphere shows an artificial pattern.

For validation of the ISIMIP3a run, see Boulange et al. (2023).

Number of vertical layers: One layer but the depth varies by climate zone. As of ISIMIP Phase 3, the soil layer configuration was changed by adopting the climate zone-specific parameter optimization presented in Yoshida et al. (2022). H08 now has one climate-zone-specific soil depth and maximum soil moisture holding capacity. Based on the discussion in Yoshida et al. (2022), the climatic classification of Dc (subarctic) was further separated into six subregions. Because they are separated by meridians (e.g., 60°E or 90°E), the distribution at high latitudes in the Northern Hemisphere shows an artificial pattern. The spatial soil depth distributions are given in the attachment below.

Exceptions: H08 does not have “2015soc-from-histsoc” simulations as 2015soc simulations start with spinoffs. This is because the current version of H08 doesn’t have a “restart” function, hence we cannot start a simulation using the end values of another simulation. Similarly, all future period simulations start with spin-up in 2015 instead of continuing from the historical period. However, for pi-controlled simulations, the future period is in continuation from the historical period.

Exceptions: - Since H08 does not separate industrial water into electricity and manufacturing, total industrial water is reported in manufacturing file. - Due to limitation in research resources, we have simplified the protocol as follows - PI Control: We took Option 2 (fix at 2005) for the pre-industrial and historical periods. - PI Control: Accidentally the original simulation terminated at the end of 2290/1/1. There might some gaps in fluxes and state variables between 2290 and 2291 since two simulation are not perfectly consistent. - RCP2.6 and RCP6.0: We took Option 2 (fix at 2005) for the historical periods - RCP2.6 and RCP6.0: We calculated historical and future periods independently: there might some gaps between the results of 12/31/1860 and 1/1/1861 and those of 12/31/2005 and 1/1/2006.

How is vegetation represented?: Each land cell is subdivided into four land use (double-cropping irrigated cropland, single-cropping irrigated cropland, rain-fed cropland and natural use). Crop growth depends on given meteorological conditions. [For nosoc run] Natural use: Globally uniform. No-specific land type is assigned, as known as Manabe's bucket. [For pressoc run] Croplands: Fixed cultivars according to HYDE/MIRCA at 2000 with fixed planting dates. Geographical distribution of irrigated/rainfed cropland was based on HYDE/MIRCA at 2000. We assumed the geographical distribution of double-cropping cultivation was based on Siebert et al. (2005). Natural use: Globally uniform. No-specific land type is assigned, as known as Manabe's bucket. [For varsoc run] Croplands: Changing cultivars according to HYDE/MIRCA with fixed planting dates. Geographical distribution of irrigated/rainfed cropland was based on HYDE/MIRCA at a given year. We assumed the geographical distribution of double-cropping cultivation was fixed throughout the period and based on Siebert et al. (2005). Natural use: Globally uniform. No-specific land type is assigned, as known as Manabe's bucket.