Hydrological modelling with reservoir operation – An assessment in the context of climate change adaptation

Abstract:

The reservoir operations would seem to have a potential impact in controlling the regional and even continental-scale hydrology by partly mitigating the inter-annual and inter-seasonal variations in river flow. Despite this fact, the reservoir operations are not well expressed in global hydrological models due to the lack of data and the complexity of reservoir operations and hence, there is limited knowledge about their adaptation potential under a changing climate. To fill this knowledge gap, we employed the H08 global hydrological model, (which includes reservoir operation) to evaluate the adaptation potential of reservoir operation using a case study in the Chao Phraya River basin (CPRB). The future climate scenarios were constructed from the bias-corrected outputs of three general circulation models from 2080-2099 under RCP4.5 and RCP8.5.

This study mainly addressed three key questions of concern in the CPRB as follows: (i) Whether the existing water storage infrastructures are sufficient to dampen the inter-seasonal flow variations under a changing climate, (ii) Whether the construction of a new infrastructure (i.e., under planning) could lessen the risk of flooding, and (iii) Whether the existing and new infrastructures together could mitigate the effect of climate change by doubling their storage capacity. The results revealed that the wet season monthly mean discharge has increased by 36% and 63% in RCP4.5 and 8.5 scenarios, respectively, from the historical discharge, whereas the dry season discharge showed relatively low variation. The existing reservoir operation reduced the wet season monthly mean discharge by 25% in the lower basin and substantially improved the dry season flow in both scenarios. Further, the effect of the new dam in reducing the daily peak discharge was evaluated and its effect was negligible (0-5%) in the lower basin. The number of flooding days (daily peak discharge exceeded the channel capacity) in the basin were reduced to 112 from 227 under RCP4.5 and the same under RCP8.5 was 146 (reduced from 357 days) after doubling the capacity of the existing and new reservoirs. This indicates that the change in flood flows due to climate change were larger than those achieved by the combined action of the existing and new reservoir operations and thus there is a need for other adaptation options.