Makran-Meteorology
Siberian high pressure
It enters the country from the northeast and north
causes cold weather in the cities of Greater Khorasan, as well as increased pressure, clear skies, few clouds, changes in diurnal temperature, and large fluctuations.
Only in the case of the entry of active, low-pressure, and humid western systems can we expect their penetration into the country and rainfall. Otherwise, the country's share of this high-pressure system will be the same extreme cold, lack of cloudiness, changes in daily temperature, and clear skies.
Mediterranean and Western systems
Almost all winter precipitation in the country, especially in the studied region, originates from this Mediterranean system.
Humid, active, low-pressure Mediterranean air masses, crossing Europe, the Mediterranean Sea, and gaining moisture, enter the country from the northwest and west.
With good and continuous rainfall, these systems saturate the northwestern and western regions and gradually reach the northeastern and finally the southeastern regions.
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However, this only happens when the activity and strength of these fronts are high and heavy. Otherwise, Sistan and Baluchestan province will only experience dust, soil, and sandstorms.
Monsoons
The southeastern monsoons are the source of a small amount of summer precipitation in the southeastern part of the country (studied region).
The intense summer heat in the Indian subcontinent and Pakistan causes the air to rise. At the same time, humid and relatively cooler air over the Indian Ocean moves towards the land to replace the rising air.
This causes heavy monsoon rains to occur due to the ascent over the Himalayas. If this also happens with Pakistan.
waves of humid and heavy oceanic air also reach the southeast, Sistan and Baluchestan province, and irrigate the studied region. This is why we have some rainfall throughout the year, especially in summers, in these regions (despite the rest of the central regions).
Analysis of Meteorological Statistics in the South Baluchistan Basin.png)
A total of 2 synoptic stations, 3 climatology stations, 19 rain gauges, and 15 evaporation stations belonging to the Meteorological Organization and the Ministry of Energy are operating in this basin. In addition, there are 6 stability stations in the Kahriz, Pishin, Kajdar Sarbaz, Takht Malek Chabahar, and Qasr Qand stations in the South Baluchistan basin.
The observation period of the mentioned stations varies between 2 to 3 years. Chabahar and Bahukalat stations have the longest statistical period, and the minimum statistical period is related to the Bandini station.
Due to the accuracy of the statistics of Sarbaz, Chabahar, and Bahukalat stations, the statistics of these stations have been accepted as accurate and basic data, and the calculations related to the factors have been performed.
Such studies have been mostly carried out on the estimation of annual rainfall statistics, and the analysis of temperature, relative humidity, wind, sunshine hours, evaporation, rainfall, and climate of the basins have been investigated in order.
Analysis of Evaporation Statistics in the South Baluchistan Basin
A total of 15 evaporation stations are operating in the basin. The statistical period in the stations varies between 2 and 35 years. The longest statistical period is in Chabahar and Bahukalat stations, which are located at 10 and 35 meters above the free sea level, respectively. For the cold months of the year when evaporation pan measurements are not performed, correlation relationships are established between the monthly average evaporation and the monthly average temperature of the evaporation stations.
Evaporation gradient
From the long-term average evaporation of the stations and their topographic height, the relationship between evaporation height and topographic height has been calculated for the studied basin.
Ep = 3/45H+2909
r = 0/84
n = 8
EP is the average annual evaporation in millimeters, H is the topographic height of the location in meters, r is the correlation coefficient, n is the number of stations
Evaporation Isohyets
Due to the limited number of stations, evaporation data is not available in many areas. Evaporation is estimated directly using the relationship between evaporation gradient and topographic height. Using the annual average evaporation from class A pan in a reference period of existing stations and auxiliary points, it is drawn based on altitude, topography, and climate change. Evaporation stations with annual evaporation rates and intervals of evaporation isohyets are in the year. The highest evaporation from the pan is related to the Kahir station (4400 mm isohyet band). The lowest station in Tang Sarhe (2200 mm isohyet band) passes through that area.
Evaporation from a free water surface
The evaporation rate from a free water surface can be estimated using the evaporation rate from a class A pan and a conversion coefficient that takes into account the climatic conditions and the different months of the year at each station. The conversion coefficient for evaporation from the pan is chosen between 0.65 and 0.75 for different months of the year. A higher coefficient is used for the cold months of the year (November to February) and a smaller coefficient is used for March to October. Potential evapotranspiration is estimated using the Blaney-Criddle and Thornthwaite-Mather methods.
Evaporation from the free surface of water - the values of evaporation from the free surface of water from the basin and by the Blaney-Cridel method in the evaporation stations of the South Baluchistan catchment
The Blaney-Criddle method
The Blaney-Criddle method is one of the oldest methods for estimating potential evapotranspiration. ET0 is the potential evapotranspiration in millimeters per day. P is a coefficient related to the length of the day or the annual percentage of sunshine hours in the month. T is the mean monthly temperature in degrees Celsius.
ET0 = P(0/46t + 8/1)
The Thornthwaite-Bilan method
In this method, potential evapotranspiration is calculated for each month of the year.
The method is based on the mean monthly temperature and is as follows:
Im is the heat index for each month, and Tm is the mean monthly air temperature in degrees Celsius. The annual heat index (I) is obtained by summing the monthly heat indices of the year.
The calculation of PET for each month is based on the assumption that each month has 30 days and each day has 12 hours of daylight.
The potential evapotranspiration (PET) for each month of the year, in millimeters, is calculated using the following formula:
Climatic characteristics
South Baluchistan is characterized by hot and long summers and mild winters. Rainfall in the study area occurs in two distinct seasons: winter and summer rainfall
Due to the hot desert climate, rainfall in this region follows the characteristics of rainfall in arid regions. Most rainfall events are of short duration, relatively high intensity and limited extent.
The majority of rainfall occurs in winter. Spring and summer rainfall is accompanied by thunderstorms and consists of several moving cells.
The major part of this basin (South Baluchistan) is mountainous. In the plain areas located near the Oman Sea, there are relatively vast and extensive plains such as the Pir Sohrab, Bahu Kalat and Nogor, Kahrir and Chabahar Bandini plains.
Due to the fine-grained alluvium in these plains, there are no large and extensive groundwater resources, and therefore irrigated agriculture has not been widely developed under current conditions. However, the construction of dams such as Pishin, Shi Kolak, Zirdan, and Kahrir dams will provide the possibility of developing irrigated agriculture.
In the northern parts of this basin, irrigated agricultural and orchard activities are carried out on a limited scale in the alluvium and terraces of the river margins in the areas of Sarbaz, Rask and Qasr Qand, Nikshahr, Fanuj, Bent Hangam and Ayrafshan, using the surface and groundwater of these rivers.
