The experimental basins in the Jizera Mountains were established at the beginning of the 1980th as a result of the forest devastation due to acid rain and repercussions of following human activities during its disposal with the aim to gain data for the quantification of runoff conditions changes in a changing environment. Seven small catchments with an area from 1.87 km2 to 10.6 km2 are situated in the spring regions in an elevation from 700 m a.s.l. to 1100 m a.s.l. in the catchments of the Černá Nisa, Kamenice, Jizerka and Směda streams. The long-term average annual temperature in the elevation of 780 m a.s.l. is +4.4°C, the long-term annual precipitation sum fluctuates between 1300 mm and 1800 mm. The Jizera Mountains are known for numerous intensive rainfalls in the summer period. The administrator of the experimental basins is the Czech Hydrometeorological Institute (CHMI), Department of Hydrological Research, Experimental Base Jablonec nad Nisou, which performs all operative activities and basic processing of data. In the basins, the monitored elements are water stages and discharges in rivers, surface water quality, rainfall, snow depth and snow water equivalent and climatological parameters. The following contribution gives an overview of information obtained from the hydrological research in the period 1981 - 2004. and Příspěvek se zabývá přehledem poznatků z hydrologického výzkumu v období let 1982-2005 v experimentálních povodích Českého hydrometeorologického ústavu (ČHMÚ) v imisně poškozené oblasti Jizerských hor. Základnu tvoří 7 malých povodí s rozlohou od 1,87 km2 do 10,6 km2 celkové plochy 37 km2 . Všechna povodí leží ve vrcholové části Jizerských hor v Chráněné krajinné oblasti Jizerské hory, na rozvodí řek Labe a Odry. Nadmořská výška povodí se pohybuje mezi 700 až 1100 m. Správcem povodí je Oddělení hydrologického výzkumu, pracoviště Jablonec nad Nisou. Zpočátku byly práce zaměřeny převážně na získání co největšího počtu informací o srážkách, sněhu, množství a jakosti povrchové vody. Po roce 1995 byl monitoring rozšířen na více parametrů hydrologické bilance, sledování klimatických prvků a složek hydrologického procesu. Následně byl upřesňován jejich režim i jejich prostorové rozložení. Byla studována problematika rozdílnosti akumulace a odtávání sněhu na mýtině a v lese a odtoková a kvalitativní odezva na srážkovou činnost a tání sněhu. Za pomoci hydrologických a chemických modelů byly hledány odhady změn jejich závislosti na změně vegetačního pokryvu.
Hydrologic cycle in the Liz catchment is described with an anomaly in the vegetation seasons 1992-1996. Experimental catchment Liz is located in the Šumava Mts. in the Czech Republic. The fully forested watershed is covered by mature spruce forest, and its basic characteristics are as follows: drainage area 0.99 km2, mean discharge 0.01m3 s-1, runoff coefficient 0.38, mean annual air temperature 6.30 oC, average slope 17 %, basin length 1.45 km, water course length 1.43 km, elevation 828-1074 m a.s.l., precipitation sum 851 mm year-1, and runoff depth 324 mm year-1. Air temperature, precipitation, global radiation, and discharge in the closing profile are measured in the catchment. It is characteristic for hydrologic cycle in the catchment that the share of seasonal sums of both the global radiation and temperature was nearly constant in 1983-2000. However, the seasonal sums of both the global radiation and temperature were changed considerably in 1983-2000. Similarly, the share of seasonal sums of both the rainfall and runoff was nearly constant in 1983-1991 and 1997-1999. An anomalous course of climate was registered in 1992-1996, manifested by a deviation on the double mass curve of the seasonal sums of rainfall and runoff. Stabilised elsewhere, the ratio of rainfall and runoff is changed during the vegetation seasons 1992-1996. Starting from the 1997 season, this ratio has obtained the value held before 1992. The reason of the 1992-1996 anomaly of hydrologic cycle in the experimental catchment had to be significant external phenomenon, most likely explosion of the Mount Pinatubo volcano in Philippines on June 15, 1991. and Hydrologic cycle in the Liz catchment is described with an anomaly in the vegetation seasons 1992- 1996. Experimental catchment Liz is located in the Šumava Mts. in the Czech Republic. The fully forested watershed is covered by mature spruce forest, and its basic characteristics are as follows: drainage area 0.99 km2 , mean discharge 0.01m3 s -1, runoff coefficient 0.38, mean annual air temperature 6.30 ºC, average slope 17 %, basin length 1.45 km, water course length 1.43 km, elevation 828-1074 m a.s.l., precipitation sum 851 mm year-1, and runoff depth 324 mm year-1. Air temperature, precipitation, global radiation, and discharge in the closing profile are measured in the catchment. It is characteristic for hydrologic cycle in the catchment that the share of seasonal sums of both the global radiation and temperature was nearly constant in 1983-2000. However, the seasonal sums of both the global radiation and temperature were changed considerably in 1983-2000. Similarly, the share of seasonal sums of both the rainfall and runoff was nearly constant in 1983-991 and 1997-1999. An anomalous course of climate was registered in 1992-1996, manifested by a deviation on the double mass curve of the seasonal sums of rainfall and runoff. Stabilised elsewhere, the ratio of rainfall and runoff is changed during the vegetation seasons 1992-1996. Starting from the 1997 season, this ratio has obtained the value held before 1992. The reason of the 1992-1996 anomaly of hydrologic cycle in the experimental catchment had to be significant external phenomenon, most likely explosion of the Mount Pinatubo volcano in Philippines on June 15, 1991.