HW02 Hydrological Model Intercomparison for Climate Impact Assessments

IAHS (Hydrology)

23-Jun-2015, 15:00 - 16:30

Abstract content:

Propagation of biases in humidity in the estimation of global irrigational water

Future projections on hydrological environments under a changing climate are highly dependent on meteorological data derived from general circulation models (GCMs). Since climate projections include biases, bias correction is widely used to adjust meteorological elements, such as the atmospheric temperature and precipitation, but less attention has been paid to biases in humidity. In this study, we examined how the biases remaining in the humidity data propagate into results of impact assessment of future climate change. We mainly focused on impacts on the estimation of irrigational water using the global hydrological model (GHM) H08. To determine the effects of humidity bias across GCMs, we used meteorological data sets to which a state-of-the-art bias correction method was applied except to the humidity.

We found that differences in the monthly relative humidity of 11.7 to 20.4 %rh from observations across the GCMs caused the estimated irrigational water abstraction from rivers to range between 1217.7 and 1341.3 km3/yr for 1971-2000. Differences in humidity also propagate into future projections. We also performed another set of experiments to examine whether bias correction of the humidity can reduce uncertainties in irrigational water across the GCMs. The results showed that bias correction, even with a primitive methodology that only adjusts the monthly climatological relative humidity, helped reduce uncertainties across the GCMs.

Although the GHMs have different sensitivities to atmospheric humidity because of the implementation of different types of potential evapotranspiration formulae, bias correction of the humidity should be included in hydrological analysis, particularly for the evaluation of evapotranspiration and irrigational water.
Y. Masaki1, N. Hanasaki2, K. Takahashi3, Y. Hijioka3.
1National Institute for Environmental Studies, Tsukuba, Japan.
2National Institute for Environmental Studies, Center for Global Environmental Research, Tsukuba, Japan.
3National Institute for Environmental Studies, Center for Social and Environmental Systems Research, Tsukuba, Japan.


impact assessment     climate change     bias correction     humidity     evapotranspiration     irrigational water