Pavol Miklánek, Alojz Koníček, Pavla Pekárová
Institute of Hydrology, Slovak Academy of Sciences, Bratislava, Slovakia
ABSTRACT
The paper presents the analysis of the annual and monthly long-term water balance elements in the experimental agricultural microbasin Rybárik of the IH SAS. The analysis is based on the data series of water years 1964/1965-2000/2001. The mathematical relations between precipitation and runoff were developed for the vegetation and non-vegetation seasons. Monitoring of the basic water elements in the experimental agricultural basin Rybárik has shown a decreasing trend of both annual and seasonal precipitation and runoff over the last 37 years (precipitation by 2.7 mm/year, runoff by 3.3 mm/year on average). The decrease of both precipitation and runoff in the non-vegetation season is higher than in the vegetation season.
Keywordsexperimental basin, long-term water balance, trends, Rybárik MEAN ANNUAL WATER BALANCE CHARACTERISTICS
The Institute of Hydrology SAS operates several experimental basins (Herrmann et al., 1997; Kostka and Holko, 1996; Holko and Kostka, 1999). The experimental microbasin Rybárik (Fig 1) is an agricultural basin extending over 0.12 km2 (15 % grassland, 85 % arable land). More details about the basin were given by Koníček et al. (1997), Bača (2001, 2002).
Jelšové
Mošteník
FAPŠOVÁ
DUŠIANICA
PAULECOVÁ
KUDLOVÁ CINGELOVÁ
LACKOVÁ GALANOVEC
RYBÁRIK LESNÝ
LEGEND
Water stage recorder Meteorological station 1 km
100m R y b á r i k
L e s n ý
Runoff gauge
Fig 1: Location of the experimental basins in the Strážov highlands.
The mean annual precipitation over the study period was 741 mm. Maximum annual precipitation was 996 mm in the water year 1965/1966 (in Slovakia the water year starts in November of the previous year). The minimum annual precipitation was observed in 1972/1973 and only reached 539.6 mm.
The long-term mean annual discharge of Jelšové creek at the Rybárik station is 0.877 l.s-1, with a mean annual specific yield of 7.31 l.s-1km-2 (1964/1965–2000/2001). The minimum mean annual discharge was observed in 1991, Qmin = 0.42 l.s-1, and the maximum was observed in 1966, Qmax = 1.67 l.s-1. The yearly water balance components of the experimental microbasin Jelšové (Rybárik) are shown in Table 1 for the period of water years 1964/1965–2000/2001. Evapotranspiration was calculated from measured precipitation and runoff depth. The whole period 1964/1965–2000/2001 was characterised by a rapid decrease of available water. The deviations from the long-term mean annual discharge 1964/65–2000/2001 are evident in Fig 2.
Table 1: Annual water balance of the Rybárik basin during the years 1964/1965 - 2000/2001 P - annual precipitation, R - annual runoff depth, ET - annual evapotranspiration as difference P-R, Qa - average annual discharge, q - specific yield, cs - coefficient of symmetry (decades), cv - coefficient of variation (decades).
Year P
1965 872.4 297.3 575.1 1.13 9.43 0.34 6.8
1966 996.0 437.9 558.1 1.67 13.89 0.44 8.6
1967 720.9 316.3 404.6 1.20 10.03 0.44 8.3
1968 821.1 277.0 544.1 1.05 8.78 0.34 7.8
1969 578.7 169.5 409.2 0.64 5.37 0.29 0.81 0.28 7.6
1970 854.9 246.1 608.8 0.94 7.80 0.29 0.93 0.28 7.5
1971 610.3 232.2 378.1 0.88 7.36 0.38 -0.08 0.20 7.9
1972 872.7 261.6 611.1 1.00 8.30 0.30 0.62 0.24 8.3
1973 539.6 190.4 349.2 0.72 6.04 0.35 0.92 0.25 8.3
1974 882.4 325.1 557.3 1.24 10.31 0.37 1.15 0.22 8.4
1975 721.3 275.0 446.3 1.05 8.72 0.38 1.12 0.22 8.4
1976 704.7 212.2 492.5 0.81 6.73 0.30 0.98 0.22 8.4
1977 912.5 378.5 534.0 1.44 12.00 0.41 1.12 0.23 7.8
1978 736.9 208.0 528.9 0.79 6.60 0.28 1.28 0.20 6.6
1979 738.2 246.8 491.4 0.94 7.83 0.33 0.37 0.27 7.6
1980 791.2 251.9 539.3 0.96 7.99 0.32 0.54 0.27 6.3
1981 841.7 261.2 580.5 0.99 8.28 0.31 0.57 0.27 7.7
1982 671.2 215.1 456.1 0.82 6.82 0.32 -1.90 0.19 7.4
1983 710.7 249.9 460.8 0.95 7.92 0.35 -2.20 0.18 8.8
1984 702.6 120.8 581.8 0.46 3.83 0.17 -1.41 0.21 7.5
1985 750.6 246.5 504.1 0.94 7.82 0.33 -0.79 0.24 6.8
1986 796.5 199.0 597.5 0.76 6.31 0.25 -0.46 0.29 7.6
1987 745.3 241.0 504.3 0.92 7.64 0.32 -0.50 0.29 7.1
1988 768.5 247.7 520.8 0.94 7.85 0.32 -0.04 0.31 8.4
1989 699.5 167.5 532.0 0.64 5.31 0.24 -0.17 0.31 8.8
1990 641.2 139.7 501.5 0.53 4.43 0.22 -0.03 0.31 8.7
1991 552.4 109.1 443.3 0.42 3.46 0.20 0.23 0.34 8.1
1992 618.5 226.6 391.9 0.86 7.19 0.37 0.51 0.33 9.3
1993 569.3 122.7 446.6 0.47 3.89 0.22 0.65 0.32 8.5
1994 925.9 293.0 632.9 1.11 9.29 0.32 0.63 0.32 9.8
1995 666.1 210.3 455.8 0.80 6.67 0.32 0.37 0.30 9.3
1996 742.7 127.1 615.6 0.48 4.03 0.17 0.12 0.27 8.3
1997 711.2 186.0 525.2 0.71 5.90 0.26 7.6
1998 743.1 212.1 531.0 0.81 6.73 0.29 8.2
1999 652.4 172.6 479.8 0.66 5.47 0.26 9.1
2000 684.8 194.5 490.3 0.74 6.17 0.28 9.5
2001 858.2 260.7 597.5 0.99 8.27 0.30 8.3
mean 740.7 230.5 510.2 0.88 7.31 0.31 0.64 0.30 8.1
min 539.6 109.1 349.2 0.42 3.46 0.17 -2.20 0.18 6.30
max 996.0 437.9 632.9 1.67 13.89 0.44 1.28 0.34 9.80
Fig 2: Deviations of the mean annual discharge in individual years from the long-term mean annual discharge 1965–2001, Rybárik.
Trends of precipitation and runoff in vegetation and non-vegetation seasons
The basic water balance elements show the following trends in 1964/65-2000/01:
P (mm) = 791.4 – 2.67 x (precipitation) (1)
R (mm) = 293.9 – 3.34 x (runoff) (2)
ET (mm) = 497.5 + 0.67 x (evapotranspiration) (3)
where: x - order of the year, 1...37, starting with 1965.
The relations indicate a significant decreasing trend of annual precipitation and runoff in the basin during the last 37 years. The following relations were found for vegetation (Pv, Rv) and non-vegetation (Pnv, Rnv) seasons:
Pnv (mm) = 338.3 – 2.39 x (4)
Pv (mm) = 453.1 – 0.28 x (5)
Rnv (mm) = 200.3 - 2.39 x (6)
Rv (mm) = 93.6 - 0.94 x (7)
The results are presented in Figs 3 and 4. Precipitation significantly decreases in the non-vegetation period, while the decrease in the vegetation period is much lower. Runoff in the non-vegetation season decreases by 2.4 mm annually on average from 1965 to 2001, while in the vegetation period it only decreases by 0.9 mm.
Evapotranspiration, computed as the difference between precipitation and runoff, remains constant in the non-vegetation season and increases in the vegetation season.
100 200 300 400 500 600 700
1 3 5 7 9 11 13 15 17 19 21 2 3 25 27 29 31 33 35 37 N
Precipitation [mm]
XI.-IV.
V.-X.
Fig 3: Trend of precipitation during the vegetation and non-vegetation seasons.
0 50 100 150 200 250 300
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 N
Runoff [mm]
XI.-IV.
V.-X.
Fig 4: Trend of runoff during the vegetation and non-vegetation seasons.
0 10 20 30 40 50 60 70 80 90 100
P, R [mm]
XI XII I II III IV V VI V II VIII IX X
Month
P [mm]
R [mm]
Fig 5: Mean monthly precipitation and runoff (in mm) in the period of water years 1964/65 - 2000/2001.
Mean monthly water balance characteristics
From the point of view of monthly values, the highest precipitation occurs in June (97.9 mm) and the lowest in February (37.5 mm). Maximum runoff occurs in March (41.4 mm), and minimum runoff is observed in November (8.8 mm).
Table 2: Mean monthly runoff coefficients km [%], mean monthly precipitation Pm [mm], mean monthly runoff depth Rm [mm], mean monthly contribution to the mean annual runoff depth
Rm/Ra[%], and other statistical characteristics related to Rm, period 1964/1965-2000/2001.
XI XII I II III IV V VI VII VIII IX X
km 20.3 38.6 55.0 88.1 97.9 41.5 21.9 16.7 15.3 15.4 13.4 20.4
Pm 58.7 58.9 44.3 37.5 42.3 51.2 70.2 98 87.2 78.1 66 48.2
Rm 11.9 22.8 24.4 33.1 41.4 21.3 15.4 16.3 13.3 12.0 8.8 9.8
Rm/Ra % 5.1 9.9 10.6 14.6 18.0 9.2 6.7 7.2 5.5 5.3 3.4 4.3
Min 1.9 3.4 2.0 4.5 8.4 5.0 3.6 3.5 2.5 1.3 1.1 1.2
Max 37 118 88 113 96 61 46 56 75 120 35 102
Cs 1.12 2.83 1.54 1.38 0.75 1.47 1.81 1.44 3.46 4.38 2.67 4.89
Cv 0.804 0.924 0.852 0.785 0.590 0.592 0.679 0.778 1.021 1.719 0.855 1.728 Cs is coefficient of skewness, Cv is coefficient of variation
The mean annual runoff depth was 230.5 mm and the mean runoff coefficient was 31.1% in the 1964/65–
2000/01 period. Maximum runoff is related to the snowmelt period (33.1 mm in February, and 41.4 mm
in March). About 1/3 of the annual runoff occurs during these two months (32.6 %). The runoff coefficients are also highest during February and March: 0.88 and 0.98, respectively. The minimum runoff coefficients occur in the summer: 0.153 and 0.154 in July and August, respectively. The mean monthly values of precipitation and runoff are shown in Fig 5. The mean monthly runoff coefficients (km) and the mean monthly contribution to mean annual runoff are provided in Table 2.
Long-term monthly water balance
In Table 3 the values of long-term monthly water balance elements are shown. Precipitation and runoff are measured values. Monthly evapotranspiration was calculated from the annual water balance (ET= P-R) proportionally distributed between months according to the monthly evaporation observed in the neighbouring areas. The storage of water (S) in the agricultural microbasin increases from August to January, while from February to August the accumulated water storage decreases. Runoff (R) and evapotranspiration (ET) is augmented by soil moisture and groundwater until July-August. The course of the long-term water balance elements is presented in Fig 6.
Table 3: Mean monthly water balance elements of Rybárik (Jelšové) basin, period 1965–2001.
XI XII I II III IV V VI VII VIII IX X Year
P [mm] 58.7 58.9 44.3 37.5 42.3 51.2 70.2 98.0 87.2 78.1 66.0 48.2 740.7 R [mm] 11.9 22.8 24.4 33.1 41.4 21.3 15.4 16.3 13.3 12.0 8.8 9.8 230.5 ET [mm] 7.1 2.6 2.6 9.7 24.0 40.3 76.0 99.5 103.6 75.5 40.8 28.6 510.2 Diff=P-R-ET 39.7 33.6 17.4 -5.2 -23.1 -10.4 -21.1 -17.9 -29.7 -9.4 16.3 9.8 0.0 S 19.7 53.3 70.7 65.4 42.3 32.0 10.8 -7.0 -36.7 -46.1 -29.8 -20.0
ET [%] 1.4 0.5 0.5 1.9 4.7 7.9 14.9 19.5 20.3 14.8 8.0 5.6 100.0
ET+R 19.0 25.3 26.9 42.8 65.4 61.6 91.4 115.8 116.9 87.5 49.7 38.4 740.7
-60 -40 -20 0 20 40 60 80 100 120 140
XI XII I II III IV V VI VII VIII IX X
[mm]
P [mm]
ET+R R [mm]
S Jelsove: Rybarik 1964/65-2000/01
+ - - +
Fig 6: Course of the water balance elements computed from the long-term monthly averages in the Rybárik basin, period 1964/1965–2000/2001.
Relation between runoff and precipitation
The relation between seasonal runoff and precipitation is linear in the non-vegetation season (Rnv, Pnv), and quadratic in the vegetation season (Rv, Pv) in the Rybárik basin (see also Figs 7a, b):
Rnv (mm) = 0.6594 Pnv – 38.4 (8)
Rv (mm) = 0.0013 Pv2 – 0.795 Pv + 154.53 (9)
where: Rnv, Pnv - seasonal runoff and precipitation in November-April, and Rv, Pv - seasonal runoff and precipitation in May-October.
a)
Fig 7: Seasonal precipitation - runoff relation in (a) the non-vegetation and (b) the vegetation season (years 1965-2001).
CONCLUSION
Monitoring of the basic water elements in the experimental agricultural basin Rybárik has shown a decreasing trend of both annual and seasonal precipitation and runoff in the past 37 years (precipitation by 2.7 mm/year, runoff by 3.3 mm/year on average). The decrease of both precipitation and runoff in the non-vegetation season is higher than in the non-vegetation season.
Annual and seasonal linear trend equations were found (Eq. (1) - (7)). The long-term monthly water balance was also estimated in Table 3 and Fig 6. Seasonal relations between precipitation and runoff were developed as well (Eq. (8) - (9)).
ACKNOWLEDGEMENT
Financial support from the Slovak Scientific Grant Agency Project 2016 is gratefully acknowledged.
REFERENCES
Bača, P. (2001) Analysis and modeling of the surface runoff and erosion process in small basin. (in Slovak.) Acta Hydrologica Slovaca, 2, 1, 93-97.
Bača, P. (2002) Temporal variability of suspended sediment availability during rainfall-runoff events in a small agricultural basin. Proc. 9th ERB and NEFRIEND5 Int. Conf. Interdisciplinary Approaches in Small Catchment Hydrology: Monitoring and Research, Slovak NC IHP UNESCO / UH SAV, 198-201.
Herrmann, A., Eliáš, V., Buchtele, J., Tesař, M., Vuglinsky, V., Zhuravin, S., Holko, L., Kostka, Z., Molnár, Ľ. (1997) Process Studies. Advances in Regional Hydrology through East European Cooperation (ISBN 0948540834), Institute of Hydrology, Wallingford., 25–27.
Holko, L., Kostka, Z. (1999) Study of runoff formation in the Western Tatra mountains. Proc. Int. Workshop Experimental Hydrology with Reference to Hydrological Processes in Small Research Basins (Ed. A. Herrmann). State Hydrological Institute, St. Petersburg, 88–92.
Koníček, A., Miklánek, P., Pekárová, P. (1997) The estimation of pollutant loads from experimental microbasins during extreme hydrological events. In: Technical Documents in Hydrology, No. 14, UNESCO, Paris, 65–70.
Kostka, Z., Holko, L. (1996): Estimation of Hydrological Balance Components at Variable Conditions of the Mountainous Catchment. Proc. Ecohydr. High Mount. Areas, ICIMOD, Kathmandu, 181–186.