How many drought indicators are there? What are the features?

Nowadays, there are more studies on drought indicators in various countries around the world, and there are about 50 kinds of them

1. Precipitation.

Atmospheric precipitation is the main source of water in agriculture. Long-term scarcity of precipitation may cause insufficient soil moisture, destroy the water balance in plants, and hinder normal physiological activities, affecting growth and development and yield formation. Although atmospheric precipitation is only a part of the income item of farmland water balance, the amount of atmospheric precipitation in a certain climate region and its seasonal distribution in a certain climate area are closely related to the local dry and wet conditions, which to a certain extent reflects the satisfaction of agricultural water demand.

And precipitation data are readily available, time series.

Long, many sites for materials, and large coverage. Therefore, precipitation is still one of the commonly used indicators to evaluate agricultural drought.

Second, the difference between water supply and demand or the ratio of water supply and demand.

The difference between water supply and demand (ratio) reflects the relationship between the possible water supply and the water demand of crop groups in a certain period of time. It can make up for the shortcomings of using precipitation as a drought index to only consider farmland water income without considering water expenditure, which has certain agroclimatic significance.

3. Palmer Index (PDSI).

The formation and development of drought is a slow process of water deficit. Most climatological drought indicators only take into account the amount of water deficit over a certain period of time and are not linked to duration, making it difficult to reveal the severity of drought. Knowing the distribution of the Palmer index in each region, the drought situation in the area can be obtained by comparing the Palmer index with the drought level.

If the temporal variation characteristics are continuously analyzed, the occurrence, development, weakening and termination of drought can be seen, so as to provide a strong basis for drought monitoring and assessment.

4. Drought indicators expressed as soil moisture.

As soil evaporation and plant transpiration continuously consume water in the soil, no or significantly less precipitation can lead to soil moisture that gradually dries out. The first to cause shallow roots or crops that need more water to wilt, the drought situation further develops, the shallow root crops are seriously affected by the drought and die, and the deep-rooted crops also wither, and then lose leaves, flowers, fruits, and even die. If there is no precipitation for a long time, not only the plants will be affected, the river will be cut off, the wells will dry up, and people and animals will have difficulty drinking water, resulting in famine.

The water used by plants is mainly absorbed by plants from the soil through their root systems. If the soil is sufficiently hydrated, it can meet the needs of plant transpiration and plant photosynthesis.

and dry matter growth; On the contrary, when the soil moisture is reduced to a certain extent, the binding force of the soil to the water increases, the plant has difficulty absorbing water, transpiration is affected, the photosynthetic ability is weakened, the plant wilts, and in severe cases, it can gradually die. Therefore, soil drought is the direct cause of agricultural drought, and soil moisture content can be used as an indicator to measure the degree of agricultural drought and its impact on plant growth.

Drought indicators are generally divided into three types: early drought, mid-drought, and late drought; The characteristics of the early stage of drought, the lack of water on the soil surface, the curled up leaves of crops, in the middle of the drought, the soil water shortage is serious, the crops appear a variety of pests and diseases, the growth is slow, the leaves are yellow, in the late drought, the crops will be directly killed, and the soil will appear in a large area of agglomeration, there is no water at all, and even drought cracks.

There are generally four indicators of drought, precipitation, water supply and demand, Palmer index, and soil moisture, which is characterized by a large number of detailed data every year, which is very large and must be recorded by special personnel.

There are more than 50 kinds of water, which are confirmed by precipitation, by the difference between water supply and demand, by the Pamol index, and by soil moisture.

1.Qinling Huai River.

Spring drought is prominent in the northern region.

2.The Huang-Huai-Hai region often has drought in spring and summer, and even in spring, summer and autumn.

3.The middle and lower reaches of the Yangtze River are mainly drought and autumn drought.

4.Most of the Northwest, Northeast China.

The western part of the country suffers from drought all year round.

5.Southwest.

The spring and summer droughts have a great impact on agricultural production, and the eastern part of Sichuan often has autumn droughts.

6.South.

Droughts also occur from time to time.

7.The main reason for the formation of drought in our country.

8.Precipitation: In general, droughts are susceptible to below-average precipitation.

9.In the monsoon climate zone of China, the precipitation season in different regions forms the basis for the distribution of seasonal drought-prone areas in China.

10.In terms of water resources: there is more water and less arable land in the south of China, and less water and more arable land in the north.

11.This imbalance of water resources between regions is an important factor causing drought disasters in China.

12.Socio-economic aspect: It mainly refers to the increase in water use for industrial and agricultural production in China in recent decades.

The World Meteorological Organization (WMO) is the first to recognize the following six types of drought:1. Meteorological drought: According to the insufficient precipitation, it is expressed as the absolute value of precipitation over a specific duration.

2. Arid climate: According to the insufficient precipitation, the mold lead car is not expressed in a specific amount, but in a ratio with the average or normal value. 3. Atmospheric drought:

It involves not only the amount of precipitation, but also climatic factors such as temperature, humidity, wind speed, air pressure, etc. 4. Agricultural drought: It mainly involves soil moisture content and plant ecology, perhaps the characteristics of a specific crop.

5. Hydrological drought: the reduction of river flow, the reduction of lake or reservoir capacity and the decline of groundwater level are mainly considered. 6. Water management drought

It is characterized by water scarcity due to the actual operation of water management or the destruction of facilities. The more common definition in China is:1. Meteorological drought:

During periods of abnormal dry weather, persistent water scarcity is enough to affect the region and cause severe hydrological imbalances. 2. Agricultural drought: Climate change with insufficient precipitation can adversely affect crop yields or pasture yields.

3. Hydrological drought: periods of below-average water content in rivers, reservoirs, groundwater aquifers, lakes and soils.

There are many influencing factors:

1. Geographical location and altitude;

2. The distance from the major water systems;

3. There is a direct correlation between the drift of the earth's crustal plates;

4. Astronomical tides;

5. Local vegetation coverage level;

6. Others, such as the laws and effects of climate change, such as the greenhouse effect, etc.

Meteorological drought refers to the continuous abnormal dry weather that leads to water shortage, resulting in a severe hydrological imbalance in the fota. The most obvious manifestation is persistently lower than a certain normal level of rainfall.

According to the national standard of the People's Republic of China for the classification of meteorological drought, meteorological drought refers to the phenomenon of water shortage caused by the imbalance between evaporation and precipitation in a certain period of time, and the water expenditure is greater than the water income. Meteorological droughts are usually mainly measured by a shortage of precipitation.

The most intuitive manifestation of meteorological drought is a decrease in precipitation. The pre-rock reduction of precipitation is not only the root cause of meteorological drought, but also an important natural factor that causes other types of drought.

The areas with more severe drought are: inland areas such as the Tarim Basin and the Turpan Basin in Xinjiang, China. There are still so-called semi-arid areas, where precipitation is slightly greater than evaporation, such as Shaanxi, Gansu and most other areas. Arid zones are areas with scarce precipitation, high evaporation, and low runoff.

Arid zone refers to an area with an arid climate, accounting for about 30% of the land area, and its common characteristics are: low precipitation and high variability.

There is also a greater diurnal and annual temperature range than the general temperature, and the evaporation may be much greater than the amount of water in the fall, with more wind and sand, less cloud cover, and strong sunshine.

Water deficiency is the main restriction on plant growth, hence the spike. Due to the abundance of heat, it has the potential to become a high-yield area when irrigation water is used and fertilized.