Changes in Latvian river discharge regime at the turn of the century

Abstract

The study deals with turn-of-the-century changes in the total annual river runoff distribution and high and iow flows in Latvia, covering river basins within four hydrological districts which vary according to size and physiographical conditions. Mathematical statistical methods were applied in the analysis of river discharge data series for two study periods of 1951-2009 and 1881-2009. The present results confirm the basic statement concerning the Baitic countries that major significant changes in river runoff during the iast two decades have occurred between spring (decrease) and winter (increase) seasons. Mostly insignificant changes in summer runoff and significant/insignificant changes in autumn runoff were found. Analysis shows that a statistically significant trend of increase in low flow for the cold period and a significant trend of decrease in the high discharge and coefficient d of uneven runoff distribution were detected. Changes in river hydrological regime are mainly caused by changes in large-scale atmospheric circulation processes following climate warming, which has taken place. Latvian river hydrography has therefore changed and become more similar to Western European rivers.

Grasslands of Northern Europe and the Baltic States

“…Wet grasslands of the Northern Europe can experience nega9ve impacts due to less ice and snow cover, leading in changing moisture regime during spring. Floodplain grasslands will experience less spring flooding (Apsīte et al 2013), meaning also less possibili9es for dispersal of grassland flora and fauna which is facilitated by floods. It could partly be mi9gated by greater water availability as precipita9on is forecasted to increase for Northern Europe, thus offering opportuni9es to restore or create new wet grasslands from intensively managed drained grasslands or croplands (Joyce et al 2016).…”

Recent Change—River Run-off and Ice Cover

“…Recent studies of run-off in Latvia include those by Apsīte et al (2009Apsīte et al ( , 2013. The authors studied a 1951-2009 data series of twenty-five river hydrological stations.…”

“…4). Since the 1940s, deep cyclones have been more frequent across Lithuania during (Apsīte et al 2013) winter (Bukantis et al 2001). Consequently, winters have become warmer, long-lasting seasonal frost has decreased, and the contrast between seasons has diminished.…”

Long-term phenological data set of multi-taxonomic groups, agrarian activities, and abiotic parameters from Latvia, northern Europe

“…From the relatively narrow study of natural rhythms, phenology has developed into an interdisciplinary field of science, the application of which is constantly expanding. Phenological data are important for agriculture, forestry (Peñuelas et al, 2009), understanding ecological processes (Walther et al, 2002), human health (Dierenbach et al, 2013) (knowledge of allergen flowering times and implementation of early warning and monitoring systems can protect those affected by pollinosis and reduce economic losses due to illness), tourism, and education (Kalvāne, 2011), and on-site phenological observations are used as ground truth for satellite data calibration (Nagai et al, 2018). Additionally, phenolog-ical data are increasingly being used as bioindicators of climate change (Jochner and Menzel, 2015;Menzel et al, 2020;Ovaskainen et al, 2013).…”

“…Agrarian observations allow one to gain insight into cultural and historical events: for example, the database contains data on the initiation of grazing in Latvia. Historically, the first cattle grazing after the long winter (Latvia has 96 to 155 d frost days annually; Avotniece et al, 2017) was a significant event, which was celebrated by entertainment like traditional water fights (rumulēšanās in Latvian). Along with changes in agricultural practices, such events were no longer recorded.…”