From the perspective of nature alone, drought and drought are two different scientific concepts. Drought usually refers to the climate phenomenon that the total amount of fresh water is insufficient to meet human survival and economic development. Drought is generally a long-term phenomenon, but drought is different. It is only an occasional natural disaster, and even in areas with abundant water, it may be caused by temporary climate anomalies. Drought and drought are the main natural disasters faced by mankind from ancient times to the present. Even today, when science and technology are so advanced, their disastrous consequences are still everywhere. In particular, with the economic development and population expansion of mankind, the shortage of water resources has become increasingly serious, which has directly led to the expansion of arid areas and the aggravation of the degree of drought. The trend of drought has become a global concern.
Drought type
The World Meteorological Organization recognizes the following six drought types:
1. Meteorological drought: based on the insufficient precipitation, it is expressed as the absolute value of precipitation for a specific duration.
2. Climate drought: it is expressed in the ratio to the average or normal value, not in a specific amount, according to the insufficient precipitation.
3. Atmospheric drought: it involves not only precipitation, but also climate factors such as temperature, humidity, wind speed and pressure.
4. Agricultural drought: mainly related to soil water content and plant ecology, perhaps the behavior of a particular crop.
5. Hydrological drought: mainly consider the reduction of river flow, the reduction of lake or reservoir storage capacity and the decline of groundwater level.
6. Water management drought: it is characterized by water shortage caused by the actual operation of water management or the destruction of facilities.
The general definition in China is:
1. Meteorological drought: during abnormal dry weather period, continuous water shortage is enough to affect the region and cause serious hydrological imbalance.
2. Agricultural drought: the climate change with insufficient precipitation has enough adverse impact on crop yield or pasture yield.
3. Hydrological drought: the period when the water content in rivers, reservoirs, groundwater aquifers, lakes and soils is lower than the average water content.
Classification of drought
Minor drought
There are 16~30 consecutive days without rainfall in spring, 16~25 days in summer, and 31~50 days in autumn and winter.
Features: The precipitation is less than usual, the surface air is dry, and the soil has a slight water shortage, which has a slight impact on crops;
Moderate drought
Continuous days without rainfall, 26~35 days in summer, 51~70 days in autumn and winter.
drought
There are 46~60 consecutive days without rainfall in spring, 36~45 days in summer, and 71~90 days in autumn and winter.
A severe drought
The number of consecutive days without rainfall is more than 61 in spring, 46 in summer, and 91 in autumn and winter.
Drought warning signal
Drought warning signals are divided into two levels, which are orange and red respectively. The classification of drought index is based on the comprehensive meteorological drought index in the national standard Meteorological Drought Grade.
Causes of drought
Drought and changes in plant system distribution, temperature balance distribution, atmospheric cycle state, chemical element distribution and other system changes related to human activities are directly related to:
1. It is directly related to geographical location and altitude;
2. It is directly related to the distance between major river systems;
3. It is directly related to the slip and drift of the earth's crust plate;
4. It is directly related to astronomical tide;
5. It is directly related to the local vegetation coverage level;
6. Others
