Special Issue on Modeling of Hydroclimate and Climate Change

The Earth is fundamentally a system of dynamically interacting oceanic, atmospheric, and land components. As such, utilization of coupled models has significant advantages over the models that focus on each of the components separately and use information from other components as their boundary conditions or forcing functions/inputs. When the atmospheric and land surface hydrologic processes are modeled as a coupled system, the atmospheric inputs for the land hydrologic component, such as precipitation, radiation, and relative humidity, are automatically supplied to the hydrologic component as a result of the solution of the coupled system versus needing such atmospheric information as external input to a standalone hydrologic component model. This creates a very significant advantage in solving such outstanding problems as that of ungauged basins. When performing coupled atmospherichydrologic modeling over such basins, the unknown precipitation and other atmospheric inputs for the hydrologic component are solved as part of the coupled system, providing the crucial information for the solution of the hydrology of the ungauged basin. Similarly, linking oceanic processes with hydrologic processes or atmospheric processes may also transfer some crucial information, such as sea surface temperatures, for the effective long-term prediction of hydrologic processes in watersheds that may be far removed from the ocean, which may be the primary source of moisture supply to the particular watershed. Starting in the late 1980s and early 1990s, hydrologic engineers began to realize the value of coupled interactive modeling of hydrologic processes together with atmospheric or oceanic processes and started developing physically based regional-scale (mesoscale) coupled atmospheric-hydrologic models. Such models are called hydroclimate models. Similarly, hydrologic engineers began to utilize various statistical tools in trying to link various oceanic process indexes with the hydrologic variables to improve hydrologic forecasting. This special issue of the Journal of Hydrologic Engineering on the modeling of hydroclimate and climate change focuses on such numerical coupled atmospheric-hydrologic hydroclimate models and various statistical approaches toward modeling various hydrologic and climatic processes over large watersheds and regions for the long-term forecasting of hydrologic processes, for water resources planning, and for assessing the effect of climate change on the hydrologic regime of a region. Within the previously discussed framework, the papers in this special issue are separated into two primary categories: (1) statistical approaches toward linking various components of the earth system toward improving long-term hydrologic forecasting and (2) numerical regional-scale coupled atmospheric-hydrologic hydroclimate modeling approaches for the reconstruction of nonexistent historical hydroclimate data for utilization in water resources planning and management studies and for dynamical downscaling of global-scale coarse resolution historical climate data and future GCM climate projection data onto regions of interest at fine space-time resolution to assess the effect of climate change on the hydrologic regime and water resources of the particular regions. The papers titled “Appraisal of Statistical Predictability under Uncertain Inputs: SST to Rainfall,” “Association between Uncertainties in Meteorological Variables and Water Resources Planning for the State of Texas,” “Basis for Extending Long-Term Streamflow Forecasts in the Colorado River Basin,” and “Scaling Characteristics of Precipitation Data over Texas” fall into the category of statistical approaches. Meanwhile, the papers titled “Application for a Coupled Regional-Scale HydrologicalAtmospheric Model to Japan for Climate Change Study,” “Regional Modeling of Climate Change Impact on Peninsular Malaysia Water Resources,” “Reconstruction of Historical Atmospheric Data by a Hydroclimate Model for the Mekong River Basin,” “Upscaling of Coupled Land Surface Process Modeling for Heterogeneous Landscapes: Stochastic Approach,” “Coupled Regional Hydroclimate Model and Its Application to the TigrisEuphrates Basin,” “AWater Balance Study for the Tigris-Euphrates River Basin,” and “Impact of Water Resources Utilization on the Hydrology of Mesopotamian Marshlands” fall into the category of numerical regional-scale coupled atmospheric-hydrologic hydroclimate modeling approaches. It is the hope of this guest editor that this special issue shall become the first in a sequence of special issues on the topic of modeling hydroclimate and climate change as the field advances and matures in the future.