In last decades several studies have showed that global temperature rise has a serious impact on the global hydrological cycle. Therefore various projects and programmes are developed in many countries aimed to carry out a simulation of hydrological processes and to forecast climate change impact on river runoff in the future using several hydrological models.

The aim of this study is to apply a conceptual rainfall-runoff model IHMS-HBV for the simulation of hydrological process and explore to Latvia rivers runoff character. The simulations were based on scenarios from global climate model HadAM3H and two emission scenarios A2 and B2 for greenhouse gases from the regional climate model Rossby Centre Atmosphere Ocean.

As input data for the model daily mean-values of temperature (⁰C), precipitation (mm) and long-term monthly average evapotranspiration values at twelve meteorological station and daily river discharge (m³ s^-1) at six hydrological stations, were applied. The calibration period was selected from 1961 - 1990 and validation period from 1991 - 2000. A2 and B2 represent the period of future scenarios (2071 - 2100).

The study results allow to assess potential annual and seasonal changes in river runoff and meteorological parameters in the future to comparing between study periods 2071 - 2100 and 1961 - 1990 for the 6 studied river basins: Berze, Imula, Iecava, Vienziemite, Dursupe and Salaca. Our study results allows concluding that comparing to the control period, both scenarios A2 and B2 show the increase in the long-term mean annual air temperature and precipitation, while the mean annual river flow is forecasted to decrease in the studied river basins. Major differences in the future hydrometeorological parameters were observed according to the A2 scenario in both analyses - annual and seasonal. We can conclude that we have identified similar patterns of hydrometeorological parameters in the projections of future climate changes compared with different earlier studies in Baltic countries and Baltic Sea basin as well. It is clearly, that climate changes impact river runoff patterns in future.