Effects Of Forest Cover Change On Extreme Temperature And Precipitation In Heilongjiang Province In The Last Century

Heilongjiang Province is the largest forest area in our country,and it is also the province with the largest decrease in forest area and the largest change in nature over the past century,its accompanying extreme climate problems are also significant.In order to reveal the influence of forest cover change on extreme weather,this study simulated the effects of forest cover change on extreme temperature and extreme precipitation in the past one hundred years.Based on the forest data of 1900s?1950s?1980s and 2010s in Heilongjiang Province with the WRF/Noah-MP model,the results show that:(1)In the past hundred years,the forest cover in Heilongjiang Province decreased firstly and then increased in Heilongjiang Province.There was also a continuous decline in 1900s~1980s forest cover.The total forest area decreased by 110901.920km~2.The largest percentage of the decline in forest cover was 22.710%.1980s~2010s forest area showed an increasing trend with an increase of 30011.754km~2.(2)The reasons for the change of forest area in Heilongjiang Province are mainly caused by human beings,the reasons for the decrease in 1900s~1950s forest area were unbridled plunder of the Russia and the Japanese Imperialist and deforestation caused by population migration.The main reasons for the reduction of 1950s~1980s forest area were the low awareness of ecological and environmental protection,long-term emphasis on harvesting and contempt of cultivation and even deforestation.The increase in1980s~2010s forest area was due to the improvement of ecological and environmental protection consciousness and the implementation of the policy of returning farmland to forests.(3)The forest area decrease caused the increase of cold days(TX10),cold nights(TN10),warm days(TX90),warm nights(TN90),frost days(FD)ice days(ID)tropical nights(TR),summer days(SU)and annully minimum value of daily maximum temperature.It also caused the decrease of the annully maximum value of daily maximum(minimum)temperature in Heilongjiang Province.In space,annully maximum value of daily maximum temperature(TXx)and annully minimum value of daily maximum temperature(TNx)increased significantly in the west,spatial distributions of spring and autumn were similar to the annual,summer maximum value of daily minimum temperature increased significantly in the west,minimum value of daily minimum temperature increased significantly in the southwest and east.Winter maximum value of daily maximum temperature(TXx)and the minimum value daily minimum temperature(TNx)showed that the spatial characteristics in the southwest and midwest was decreased,south-central and north-east was increased.(4)The forest area decrease caused extreme precipitation(R95),very heavy precipitation days(R20mm),the increase of consecutive wet days(CWD).It also caused the decrease of simple daily intensity index(SDII),maximum 5-day precipitation(RX5day)and consecutive dry days(CDD).Spatially,the extreme precipitation indices were very different,The increase of R95p and CWD in the eastern region was obvious,and the decrease of RX5day,R95p and SDII in the Xiaoxing'anling area in the northwest was obvious,and the increase of CWD in Daxinganling area was obvious.