atmosphere Article The Linkage of the Precipitation in the Selenga River Basin to Midsummer Atmospheric Blocking Olga Yu. Antokhina 1,*, Pavel N. Antokhin 1 , Yuliya V. Martynova 2,3 and Vladimir I. Mordvinov 4 1 Zuev Institute of Atmospheric Optics SB RAS, 634021 Tomsk, Russia; [email protected] 2 Institute of Monitoring of Climatic and Ecological Systems SB RAS, 634055 Tomsk, Russia; [email protected] 3 Siberian Regional Hydrometeorological Research Institute, 630099 Novosibirsk, Russia 4 Institute of Solar-Terrestrial Physics, SB RAS, 664033 Irkutsk, Russia; [email protected] * Correspondence: [email protected]; Tel.: +7-952-154-4669 Received: 3 June 2019; Accepted: 21 June 2019; Published: 24 June 2019 Abstract: The linkage between atmospheric blocking (blocking frequency, BF) and total monthly July precipitation in the Selenga River Basin, the main tributary of Lake Baikal, for the period 1979–2016 was investigated. Based on empirical orthogonal functions (EOF) analysis, two dominant modes of precipitation over the Selenga River Basin were extracted. The first EOF mode (EOF 1) is related to precipitation fluctuations mainly in the Mongolian part of Selenga; the second EOF mode (EOF 2)—in the Russian part of Selenga. Based on two different modes obtained, the total amount of precipitation individually for the Russian and Mongolian part of Selenga was calculated. Correlation analysis has demonstrated that precipitation over the Mongolian part of the Selenga Basin is positively correlated to blocking over Eastern Siberia/Mongolia (80–120◦ E, ESM-BF). Precipitation over the Russian part of the Selenga Basin is positively correlated to blocking over the Urals-Western Siberia (50–80◦ E, UWS-BF) and European blocking (0–50◦ E, E-BF). However, the linkage is not stable, and after the mid-1990s, the obtained positive correlation became insignificant. The analysis has shown that the dominance of E or ESM-blocking in July was the primary driver of the existence of two precipitation modes over the Selenga River Basin. During 1996–2016, the negative trend of time coefficients of EOF 1 and 2 for precipitation in Selenga had been observed, which was characterized by displacement of positive precipitation anomalies outside the basin. At the same time, there was a weakening of the linkage between precipitation in the Selenga Basin and blocking frequency. We have revealed two wave-like modes over Northern Eurasia and the subtropical part of Eurasia corresponding to E, ESM-blocks in 1979–1995 and 1996–2016. The change of the Northern and subtropical wave modes is one of the causes for the weakening of the linkage between atmospheric blocking and precipitation in the Selenga Basin and as a consequence decreased precipitation in the Russian and Mongolian part of Selenga during 1979–2016. Keywords: Lake Baikal; Selenga River; precipitation; atmospheric blocking; empirical orthogonal functions; principal component 1. Introduction Lake Baikal is a unique natural object on the UNESCO World Heritage list. The lake is the basis of hydropower engineering in Eastern Siberia [1,2]. Since 1996, a low-water period has been observed in the basin [1,3–5]. It is the longest one throughout the history of instrumental records. In recent years the low-water has aggravated [1]. The long-term low-water period has already generated environmental and water-resource management problems [1,5] within the lake basin. For example, these problems Atmosphere 2019, 10, 343; doi:10.3390/atmos10060343 www.mdpi.com/journal/atmosphere AtmosphereAtmosphere 20192019,, 1010,, 343x FOR PEER REVIEW 22 ofof 2020 example, these problems include coastline destruction, difficulties controlling water discharge at includehydro-electric coastline power destruction, plants, diandfficulties the need controlling of reconsidering water discharge the existing at hydro-electric regulation powerrules for plants, the andAngara the needreservoir of reconsidering cascade in Russia, the existing which regulation has been monitoring rules for the the Angara water reservoir outflow cascadefrom Lake inRussia, Baikal whichsince 1963. has been Searching monitoring for the the causes water outflowof this low-water from Lake period Baikal sinceand analysis 1963. Searching of scenarios for the for causes further of thisvariations low-water in the period inflow and is essential. analysis of scenarios for further variations in the inflow is essential. TheThe decreaseddecreased inflow inflow into into Lake Lake Baikal Baikal is mainly is mainly related related to the to reduced the reduced discharge discharge in the Selenga in the RiverSelenga (Figure River1 )(Figure observed 1) observed since 1996 since [ 3–8 1996]. The [3–8]. Selenga The River Selenga is the River lake’s is the most lake’s important most important tributary. Thetributary. Selenga The Basin Selenga is located Basin in Mongoliais located and in Russia,Mongolia and and it comprises Russia, and 83.4% it ofcomprises Lake Baikal’s 83.4% catchment of Lake areaBaikal’s [9]. catchment area [9]. FigureFigure 1.1. LakeLake BaikalBaikal Basin Basin (solid (solid red red and and solid solid black black lines). lines). Selenga Selenga River River Basin Basin (solid (solid red line). red Stateline). boundaryState boundary between between Russia Russia and Mongolia and Mongolia (dashed (dashed gray line).gray line). TheThe SelengaSelenga RiverRiver contributescontributes aboutabout 50%50% ofof thethe influxinflux intointo LakeLake BaikalBaikal[ 4[4].]. AtmosphericAtmospheric precipitationprecipitation isis thethe primaryprimary sourcesource ofof thethe riverriver supplysupply [[4,8].4,8]. Most of thethe annualannual precipitationprecipitation inin thethe SelengaSelenga River Basin Basin (of (of about about 450 450 mm mm per per year) year) falls falls as asrain rain [8] [ 8from] from June–August June–August (about (about 70% 70% of the of theannual). annual). Precipitation Precipitation in each in each of ofthese these three three months months can can be be up up to to 90–100 90–100 mm [[10].10]. The mainmain dischargedischarge isis also also formed formed from from June June through through August August [4]. [4]. It features It features both both dangerous dangerous floods floods and low-water and low- periodswater periods [1,2]. The [1,2]. causes The ofcauses the decrease of the decrease in Selenga in dischargeSelenga discharge should be should searched be forsearched in the variabilityfor in the ofvariability summer of atmospheric summer atmospheric precipitation. precipitation. PrimaryPrimary drivers of of precipitation precipitation fluctuations fluctuations in inthe the Selenga Selenga Basin Basin are arestill stillnot notclear clear [4]. The [4]. Theuncertainty uncertainty is caused is caused by the by location the location of the river of the basin river at the basin border at the of bordermid-latitudes of mid-latitudes and subtropics. and subtropics.It was shown It was that shown the thatcyclones the cyclones of mid-latitude of mid-latitudess [10], [East10], EastAsian Asian monsoon monsoon front front [4], [4], and and also stationarystationary RossbyRossby waves waves [11 [11,12],12] significantly significantly affect affect the formation the formation of precipitations of precipitations over the southernover the partsouthern of Eastern part of Siberia Eastern and Siberia Mongolia and Mongolia in summertime. in summertime. Thus, precipitation Thus, precipitation fluctuations fluctuations over the basin over are,the firstbasin of all,are, driven first byof theall, atmosphericdriven by circulationthe atmospheric dynamics, circulation and the roledynamics, of thermodynamic and the role factors of (localthermodynamic convective factors precipitation) (local convective is around 10–12%precipitation) [13]. is around 10–12% [13]. BasedBased onon thethe empiricalempirical orthogonalorthogonal functionfunction analysis,analysis, itit waswas shownshown thatthat atmosphericatmospheric blockingblocking (blocks)(blocks) isis thethe mostmost significantsignificant phenomenonphenomenon ofof circulationcirculation inin mid-mid- andand subtropicalsubtropical latitudeslatitudes inin summertimesummertime overover Eurasia Eurasia [ 14[14].]. A A definition definition of of blocking blocking was was formulated formulated in 1950 in 1950 [15]. [15]. One ofOne the of main the conditionsmain conditions of blocking, of blocking, according according to Rex, 1950 to Rex, [15], 1950 is the [15], splitting is the of thesplitting westerly of the flow westerly into two flow branches into two branches enveloping the blocked region. Currently, the presence of an equivalent-barotropic Atmosphere 2019, 10, 343 3 of 20 enveloping the blocked region. Currently, the presence of an equivalent-barotropic anticyclone is considered to be an essential condition of blocking [16]. Blocks explain long-term, large-scale anomalies in meteorological parameters at mid- and subtropical latitudes [17–19]. Climatological distribution of blocking frequency over Eurasia was demonstrated in [14–16,20–22]. The links between atmospheric blocking and precipitation are described in several works [23–28]. The results of numerous papers have revealed the blocks to be the cause of both low and high precipitation. Atmospheric blocking over different parts of Eurasia during summertime in 1979–2015 was accompanied by precipitation in the adjacent parts of the arid belt, including Kazakhstan, Mongolia, Northern China, and Transbaikalia [28]. Since the studied area includes the Selenga Basin, blocks can affect the precipitation