The Hazards of Rainfall Concentration in Iran

1. Since the spatial and temporal distribution of rainfall in Iran is influenced by the
distribution of global circulation systems, the lowest change in its pattern is resulted in
the severe weather abnormalities. Therefore, spatial and temporal abnormalities of
rainfall, severe changes in rainfall intensity, and rainfall difference are the main
characteristics of Iran's rainfall. Worthy studies have been carried out in relation to the
temporal and spatial variations of rainfall, as a result, their conclusion showed that the
number of precipitation is lower but the severity is higher. The purpose of this study
was to investigate and identify changes in the number of rainy days, average daily
precipitation, rainfall variation changes and the resulting hazards in the long-term
statistical period.
2. Material and First, daily precipitation data of 53 synoptic stations with a common statistical period
from 1984 to 2013 were received from the Meteorological Organization. Then, they
were selected to determine the rainy day (precipitation at 0.1mm and above). From the
viewpoint of precipitation duration, 7 classes were identified. 1 day precipitation,
precipitation with two-day sequence, and precipitation with a sequence of 3 to 7 days of
rainfall were extracted. Cluster analysis was used to identify climatic regions and their
features. The final result was the division of the country into seven regions with the
highest intra-group similarity and the most difference among groups in terms of the
number of days. In order to identify hazards and heavy rainfall, the frequency of one
day to seven days and more, to 3 parts of short term precipitation include 1 day
precipitation, 2 days and 3 days, medium term (4 days and 5 days precipitation) and
long-term (6 days and more) was divided. Then, in order to determine the changes in the
daily rainfall of each area, first, the average daily rainfall of the short, medium and long
run rainfall was calculated and the coefficient of variation of rainfall day and average
daily precipitation for each of the areas was obtained. The final map was used in GIS
using spatial analysis for zoning. In order to provide the time and spatial distribution
pattern of precipitation in each area and to identify the severity of daily precipitation, the ratio of maximum daily rainfall to annual precipitation was calculated and analyzed.
In order to compare rainfall variations in the first 15 years of the first 15 years, the
coefficient of increasing or decreasing rainfall changes was calculated in two periods.
3. In area 1 (south and south east of the country), the number of rainy days, the average
rainfall of short-term days (precipitation of one to three days), and the medium-term
(precipitation of four and five days) decreased. The average daily rainfall in this area
was 17 days a year. In area two, the number of rainy days and the average amount of
short-term and medium-term rainfall have been decreasing. The number of rainy days
was 27 days a year with a mean precipitation of 3.1mm. In the third zone (Caspian
coastlines), it was shown that the short-term rainy days are increasing, and the longterm
and long-term periods of decline are decreasing. The number of overnight days in
this area has been the highest (113 days) per year. In area 4, short and medium rainfall
is increasing in terms of the number of days of precipitation. However, long-term
precipitation (precipitation with 6 and 7 days and more) has been decreasing. The
number of days in this area is 74 days (with an average rainfall of 4mm) per year. In
zone 5, both short-term and medium-term rainfall showed a decrease in both trends,
while the shortened rainfall is also higher in this area. The total number of days in the
study period showed a decreasing trend. The annual rainfall in this area is 39 days (with
an average rainfall of 2.3mm) per year. In area 6, the number of rainy days and the
average daily rainfall (1-3 days) is increasing. Finally, in area 7, the number of
overnight days (with a coefficient of 101) and the short run average had an increase.
The medium-term and long-term rainfall have declined. The annual rainfall in this area
was about 5mm in 66 days with an average rainfall.
4. 1. Dry and semi-arid regions of Iran include areas 1, 2 and 5 (Bandar Lengeh, Konarak,
Chabahar, Zahedan, Bandar Abbas, Bam, Zabol, Iranshahr, Kish, Abadan, Yazd, Tabas,
Fasa, Bushehr, Birjand, Kerman, Kashan, Abadeh, Semnan, Isfahan, Ahvaz, Sabzevar,
Qom, Shiraz and Torbat Heydarieh). The number of short-, medium-term precipitation
days (precipitation with a 1-day, 2-day and 3-day sequence) and medium-term
precipitation (precipitation i) has declined over the course of 30 years. Long-term
precipitation (more than 5 days) has not occurred in these areas. The average daily
rainfall in arid regions of Iran is 27 days a year. The average daily rainfall of both short
and medium term has been decreasing. The average daily rainfall was 2.3mm per day.
2. The northern coast of Iran was designated as area 3. The frequency of short-term
barge days and the average rainfall are both incremental. An increasing trend indicated
that rainfall has been severe. 9% has been added to the amount of daily precipitation.
The daily rainfall in the region is 113 days per year and the average daily precipitation
is 22.9mm.
3. Mountainous area includes areas 4, area 6 and 7 (Ardebil, Gorgan, Parsabad, Khoy,
Bojnourd, Tabriz, Quchan, Shahroud, Dashan Tepeh, Maraghea, Karaj, Qazvin,
Shahrekord, Mashhad, Orumieh, Zanjan, Hamedan, Sanandaj, Yasouj, Ilam, Khorram Abad, Arak, Hamedan Nogheh, Kermanshah and Saqqez). In the statistical period of 30
years in the mountainous areas, the number of days and average rainfall has decreased
for the medium and long term, and has been increased by the number of short-term
overnight days and short-term average rainfall. The number of rainy days in
mountainous areas is 68 days per year and the average daily rainfall is 3.74mm.
4. The ratio of maximum daily rainfall to annual rainfall in all areas is increasing. This
indicates heavy rainfall and that rainfall in the region of Iran is rising. Most rainstorms
occur within just a few days. Such anomalies in the regime of rainfall, long dryness,
destruction of vegetation, followed by flood descendants and the destruction of water
and soil resources and human facilities.