عنوان مقاله [English]
Heavy rains are among the natural hazards that knowledge of their temporal and spatial distribution helps to reduce potential damage. For this purpose, the existence of a significant relationship between widespread precipitation and topographic indices of Alborz mountainous region has been investigated. In this study, Pearson correlation test was used and in this model, the dependent variable of total daily precipitation of the study area (precipitation occurred in more than 70% of synoptic stations in the area) and the independent variable of data related to topographic indicators of the study area (station height Synoptic, station slope and direction, longitude and latitude of the station, distance from the northern baseline, distance from the ridge, average height of the station in a radius of 2.5 km, average height of eight blocks fifty km in eight geographical directions to the center of the synoptic station, height difference Its average is eight blocks from the average height of the station in a radius of 2.5 km). First, the correlation between precipitation (129 days) and topographic indices based on common synoptic stations in three seasons of winter, spring and autumn was identified and then the correlation coefficients with 95% confidence interval at a significance level less than 0.05 were investigated. Each season, a sample day with the highest correlation coefficients in the majority of topographic indices was selected as the representative of that season. The study area, which is the vast Alborz mountain range, has been divided into areas with topographic and climatic similarities due to the complexity of topography and the diversity of its climatic conditions in each area. The highest number of significant statistics in terms of temporal and spatial scale between widespread precipitation with topographic indices is related to widespread precipitation in spring with 18 cases and the lowest is related to widespread precipitation in winter with 9 cases in autumn 14 cases of significant linear relationship have been identified. Among the topographic indices, the strongest index is related to the difference between the average height of blocks 50 km from the average height of the station in a radius of 2.5 km in different directions according to different seasons of the year and Evidence of the effect of direction on inclusive rainfall in the study area and that the area is in a certain direction to receive more rain , meaning that the mass of humid air entering from the northern parts of the country, including Siberian high pressure (Babaei Fini, 1393) due to low altitude and proximity to the ground is affected The surface roughness is located and the mass of moist air entering from the northwestern and western parts of the country, including the western migratory high pressures (Qashqaei, 1375), (Moradi, 1385)) due to higher altitude and more power is less affected by surface roughness. And the region's precipitation is affected by these high-level atmospheric systems. On the other hand, widespread precipitation in the northwestern and south-central Alborz region has the highest and the lowest south-western Alborz region has a significant linear relationship with the values of topographic indices. The results of this study have a significant linear relationship with most topographic indices (22 indices out of 24 Index) with widespread precipitation to be able to estimate and predict the most effective indices affecting precipitation in the region. The two topographic indices for the station and the distance from the ridge did not enter the correlation model on any day and in any area of the study area and did not establish any significant linear relationship, albeit weakly, with the total precipitation of the area.
20 - Aifeng, Lv.; L. Zhou. 2016. A Rainfall Model Based on aGeographically Weighted Regression Algorithm for Rainfall Estimations over the Arid Qaidam Basin in China. Remote Sens, 8(311): 1-17.
21 - Alijani, B .2008. Effect of the Zagros Mountains on the Spatial Distribution of Precipitation. Journal of Mountain Science, Vol 5, No 3.
22 - Bleasdale, A; and Y.K. Chan. 1972. Orographic influences on the distribution of precipitation in Proceedings Distribution of Precipitation in Mountainous Areas. World Meteorological Organisation, Geneva, 31 July–5 August, Geilo, Norway, 326(II):140-146.
23 - Burns, J. 1953. Small-scale topographic effects on precipitation distribution in San Dimas experimental forest. Trans. Amer. Geophys, Union 34:761-768.
24 - Chaun, G.K; and J.G. Lockwood.1974. An Assessment of Topographical Controls on The Distribution of Rainfall in the central Pennines. Meteorological Magazine .103:275-287.
25 - Dhar, O. N; and P. R. Rakhecha.1980. The effect of elevation on monsoon rainfall distribution in the Central Himalayas Monsoon Dynamics. J. Lighthill, and R. P. Pearce, Eds., Cambridge University Press: 253-260.
26 - Diodato, N .2005. The Influence of Topographic Co-variables on the Spatial variability of Precipitation over Small Regions of Complex Terrain. International Journal of Climatology, 25:351-363.
27 - Donley, D. E; and R. L. Mitchell.1939. The relation of rainfall to elevation in the Southern Appalachian region. Trans. Amer. Geophys. Union, 20: 711-721.
28 - Govaerts,P.2000. Geostatistical Approaches for Incorporating Elevation into the Spatial Interpolation of Rainfall. Journal of Hydrology,228:113-129.
29 - Griffiths, G.A, and, M.J. McSaveney.1983. Distribution of mean annual precipitation across some steepland regions of New Zealand.N. Z. J. Sci., 26: 197–209.
30 - Houghton,J.G. 1979. A Model for Orographic Precipitation in the North-Centeral Great Basin.Mon.Wea.Rev,107.
31 - Hutchinson, P. 1973. The interaction ofrelief and synoptic situation on the distribution of storm rainfall in the vicinity of Dunedin. New Zealand Geogr, 29: 31-44.
32 - Konrad, C.E. 1996. Relationships between Precipitation Event Types and Topography in the Southern Blue Ridge Mountans of the Southeastern USA. International Journal of Climatology ,16:49-62.v
33 - Marquı´nez, Jorge; Javier Lastra,and Pilar Garcı´a .2003. Estimation models for precipitation in mountainous regions: the use of GIS and multivariate analysis. Journal of Hydrology, 270 :1–11.
34 - Napoli, A; A.Crespi, F. Ragone, M. Maugeri, and C.Pasquero.2019. Variability of orographic enhancement of precipitation in the Alpine region. Scientific Reports, 9(1).
35 - Prudhomme, C., and Duncan,W.R., 1999, Mapping Extreme Rainfall in a Mountainous Region using Geostatistical Techniques A Case Study in Scotland, International journal of climatology, 19, 1337-1356.
36 - Rumley, G. B. 1965.An investigation of the distribution of rainfall with elevation for selected stations in Equador. M.S. thesis, Texas A&M University, 66 pp.
37 - Singh, P; and N. Kumar . 1997. Effect of orography on precipitation in the western Himalayan region. Journal of Hydrology, 199(1–2): 183–206.
38 - Stidd, C. K, and L. B. Leopold, 1951. The geographical distribution of average monthly rainfall. Hawaii. Meteor. Monogr, 1: 24- 33.
39 - Stor, D. H; L.Ferguson.1972. The Distribution of Presipitation in Some Mountainous Canadian Watersheds : Proc.WMO Symp. On Distribution of Precipitation in Mountainous Areas. vol.11, Geilo, Norway.
40 - Spreen, W. C. 1947. A determination of the effect of topography upon precipitation. Trans. Amer. Geophys,Union, 28: 285–290.
41 - Taylor, W.G, 1996, Statistical Relationships between Topography and precipitation in Mountainous Area, Northwest Science, Vol. 70, No. 2, 164-178.
42 - Weston,K.J; G. Roy.1994.The Directional-depedence of the Enhancement of Rainfall over Complex Topography. Meteorological Applications 1:267-275