Abstract
,46(2008)Published online in J-STAGE (www.jstage.jst.go.jp/browse/HRL). DOI: 10.3178/HRL.2.46Ben-Zvi and Givati (2008 hereafter BZG) raised twopoints on model’s ability to reproduce current climato-logy and hydrology used in Kitoh et al. (2008 hereafterKYA): one is reproducibility of present-day precipita-tion amounts and its spatial distribution in the model,and the other is the streamflow that is highly affectedby human intervention in reality.Ability to reproduce current climate by global nu-merical models is steadily increasing in the past decade(IPCC 2007; Reichler and Kim 2008). BZG pointed outthat the area with simulated annual precipitation >1000 mm in KYA is much larger than the area observedand the area with simulated annual precipitation < 200mm is substantially larger than the area observed. Inthe previous global models, such as those that hadprovided climate projections in IPCC AR4 (Reichler andKim 2008), regional geographical details have not beenresolved due to their coarse resolution. Our 20-km meshglobal model, however, has for the first time the suffi-cient resolution to resolve orographic rainfall well.Exact contour lines of the model simulation in KYA donot fully match with the observations, but desertclimate where annual precipitation < 200 mm is ratherwell reproduced in the Middle East. This is in contrastto the other aforementioned climate projections withcoarser resolution.Another aspect is that, while the model resultscontain uncertainties, the observed climatology datasetused in KYA to validate the model is also subject to un-certainties. In general, rain-gauge observation is morereliable than that of satellite-derived precipitation esti-mates over the land. Hence, we used a gauge-based pre-cipitation climatology dataset, which was developedwith many more rain-gauge observations over this area(Turkey, Israel and Iran), and have compared to othermonthly precipitation products and satellite-based pre-cipitation data. See Yatagai et al. (2008) for details.However, the quality of rain-gauge-based precipitationdataset depends on the density and distribution of rain-gauge network. For example, the rain-gauge network isvery sparse over a part of the Fertile Crescent area, par-ticularly over the high mountains and vast unpopulateddesert areas. These limitations certainly caused uncer-tainties in this precipitation dataset, and then hadcreated a part of the differences between the modeledand observed precipitation presented in KYA.Second point is that in our model simulation we donot account for any human intervention such as reser-voir and groundwater use. In order to project actualstreamflow at each of the targeted basins, we need toknow about future change in anthropogenic water use,but this was not sought in KYA for the reasons statedbelow. There are some attempts in the modeling com-munity to incorporate anthropogenic water usage, suchas a reservoir operation scheme, in climate models to re-produce present streamflow. By doing that, currentstreamflow reproducibility should become better. Forthis purpose, however, scenarios for how this anthropo-genic water usage will change in the future are needed,which contains further uncertainties of societal nature.Therefore, in order to avoid further complexity, wefocused on the future change in natural climate systemand its effect on regional streamflow. The difference inthe simulated streamflow between the present-day andthe future climate can be interpreted as a first approxi-mation of the streamflow change caused by the globalwarming.In spite of all the shortcomings mentioned, our pro-jections are the first ever of naturally-driven streamflowchanges in the region, which may suffer a lot fromglobal warming as suggested by most (nearly all) ofrecent IPCC (2007) AR4 models. At the same time, this isan extremely sensitive area to lack of water. Some of thestruggles or even wars in the region had to do withproblems related to water. Hence, it is tremendously im-portant to start a serious scientific dialogue on globalwarming impacts on water in this region and we hopeour Letter served in this positive direction.
Highlights
Another aspect is that, while the model results contain uncertainties, the observed climatology dataset used in KYA to validate the model is subject to uncertainties
In order to project actual streamflow at each of the targeted basins, we need to know about future change in anthropogenic water use, but this was not sought in KYA for the reasons stated below
There are some attempts in the modeling community to incorporate anthropogenic water usage, such as a reservoir operation scheme, in climate models to reproduce present streamflow
Summary
While the model results contain uncertainties, the observed climatology dataset used in KYA to validate the model is subject to uncertainties. Second point is that in our model simulation we do not account for any human intervention such as reservoir and groundwater use. In order to project actual streamflow at each of the targeted basins, we need to know about future change in anthropogenic water use, but this was not sought in KYA for the reasons stated below.
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