Prediction of River Water Temperature and its Dependence on Hydro-Meteorological Factors

Rivers will be among the most sensitive of all ecosystems to the effects of climate change as they are heated by processes similar to those warming the Earth's atmosphere. The river water and air temperatures follow each other closely. The life cycle of lotic biota is regulated by two major physical factors: water temperature and hydraulic conditions. Any change in hydraulic pattern that leads to an alteration of the established thermal regime of a lotic ecosystem will ultimately lead to a dramatic change in the composition and survival of lotic biota. In order to assess the impacts of potential climate change on thermal regime of water bodies, it is important to know the long range forecasts for various climatic parameters. For this purpose the modelling of water discharge and forecasting of future changes are performed. This paper provides the long-term changes in the Lithuanian river water temperature according to two models and emissions scenarios. This paper evaluates the changes of warm season (May-October) water temperature and heat runoff of Lithuanian rivers (Nemunas, Merkys and Dubysa) with different thermal regimes at the end of the 21 super(st) century (2071-2100) comparing to the climate normal period (1961-1990) using two climate change models (ECHAM5 and HadCM3 global climate models and the A2 and B1 emissions scenarios) and hydrological modelling (HBV model).Original Abstract: Upes yra viena jautriausiu ekosistemu klimato kaitai, nes jas veikia tie patys siluminiai procesai, kaip ir atmosfera. Upes vandens temperatura glaudziai susijusi su oro temperatura, o ju kaita yra panasaus pobudzio. Tekancio vandens organizmu veikla reguliuoja du pagrindiniai fiziniai veiksniai: vandens temperatura ir hidraulines salygos. Bet koks hidraulinis pokytis, kuris sukelia tekancio vandens ekosistemos nusistovejusio terminio rezimo pokyti, galiausiai sukelia dramatiskus sios ekosistemos organizmu sudeties ir islikimo pokycius. Siekiant ivertinti galima klimato kaitos poveiki vandens telkiniu terminiam rezimui, svarbu zinoti ivairiu klimatiniu parametru kaitos ilgalaikes prognozes. Siuo tikslu buvo atliktas upiu nuotekio modeliavimas ir galimu pokyciu prognozavimas. Ivertinti kai kuriu Lietuvos upiu (Nemuno, Merkio ir Dubysos), turinciu skirtinga termini rezima, silto metu laikotarpio (geguzes-spalio men.) vandens temperaturos ir siluminio nuotekio pokyciai XXI a. pabaigoje (2071-2100 m.), palyginti su klimato normos laikotarpiu (1961-1990 m.), naudojant du k