| As an extreme climate-hydrological event, drought has seriously affected our socio-economicand ecological systems, presenting widely distributed and frequent situation. The disturbance ofvegetation ecosystem to drought has a tolerance range, continuing drought will produce animportant impact on the composition, structure and function of vegetation ecosystem.According to the relationship between the NDVI of natural vegetation and climatic factors,precipitation and evaporation are considered to propose the connotation and quantitativeevaluation method based on standardized index of precipitation’s evaporation improved fromPenman-Monteith equation, and evaluate the applicability of the Huang-Huai-Hai River Basin,and confirm the index of standardized precipitation’s evaporation as the index of drought innatural vegetation of the Huang-Huai-Hai River basin. Make an assessment of drought to differentnatural vegetation of the Huang-Huai-Hai River Basin, screen typical dry years and draw a typicaldry year NDVI anomaly map. We also study drought response characteristics of natural vegetationtypes of the Huang-Huai-Hai River basin from drought-sensitive month and drought-sensitivetime, assess differences in drought tolerance characteristics of natural vegetation. Specific researchresults as follows.(1) The variation tendency of regional climate factor and NDVI of natural vegetation inHuang-Huai-Hai River Basin from1982to2006is roughly the same, showed the followingbasic characteristics, the growing season precipitation decreased, rising temperatures, sunlightreduced, the average relative humidity decreased, the average wind speed decreased, while aslightly increasing trend occur in the average and maximum of growing season’s NDVI. Generallyhigh correlation coefficient of natural vegetation NDVI and temperature, it’s not necessarily thesame for sensitive climate factors of different vegetation types NDVI, the relatively largedependence on the temperature of trees and shrubs, while the grass more susceptible to theaverage relative humidity and precipitation and weaker than the temperature dependence of treesand shrub vegetation, the impact on the average wind speed of shrubs and grasses NDVI is higher than trees. The affect on regional climate of the Huang-Huai-Hai River Basin natural vegetation isminimal, but the impact of area climate of natural vegetation is relatively large. Different types ofnatural vegetation area, the variability of climatic factors are quite different. The ratio of climatevariability factor of grass-zone is biggest, and then is shrub, tree is relatively small.(2) After the calculation method is based on FAO Penman-Monteith method for improvingevaporation capacity, the applicability of standardized precipitation evaporation index of AridZone of the Huang-Huai-Hai River Basin in winter is generally improved, drought assessmentcapabilities in yearly and monthly scales have also been significantly improved. It makes up forthe weak inadequate of traditional SPEI in arid areas in assessing drought of the Huang-HuaiRiver Basin, has more advantages of drought assessment in natural vegetation of theHuang-Huai-Hai River Basin. It’s a significant trend of drought based on the interannual andyearly variation of SPEI in natural vegetation of the Huang-Huai River Basin. From1961to2011,it shows a tendency to drought in natural vegetation of the Huang-Huai-Hai River Basin in aridarea, especially for fall seasons is relatively clear (-0.08/10a), then spring, followed by summerand winter. Each vegetations occurs drought frequently in autumn, drought frequency percentageclose to20%, but in winter and spring prone to severe drought, severe drought frequencypercentage close to5%. It’s a significantly annual trend of drought in natural vegetation of theHuang-Huai-Hai River Basin from1961to2011year, especially for the average state of thenatural vegetation, the drought frequency was over15%, and then is about10%, severe droughtmore close to4%. Different vegetations, respectively, the arbor area was in drought trend, mostlymild drought dominated. Shrub area compared with aridification arbor area is obvious, and theprobability of drought occurrence was large. Grass area was in drought trend, also mild drought.The probability of a severe drought is slightly lower compared to other regions.(3) The natural vegetation NDVI of different vegetations mostly smaller than normal,corresponding to1995,1997,1999,2000and2001and other typical drought year, not for eachmonth in growing season, a strong performance in drought resistance occurs in several months.The affection by drought of tree vegetation is relatively small in August, September and October,shrub for July, August, September and October, and grass for June, July and August, and trees andshrubs different, September and October the Huang-Huai-Hai River Basin drought resistantgrasses has returned to a lower level. Huang-Huai-Hai River Basin natural vegetation droughtaffected large month for May, June and July, which, in June and July drought tree and shrub inHuang-Huai-Hai River Basin sensitive vegetation months, and are on the long-term droughtsensitive. May and September for drought-sensitive vegetation grasses month, compared toSeptember, May grasses vegetation is more sensitive to drought, and more intense response.Unlike trees and shrubs, grass vegetation growing there in the late drought sensitive period. (4) There were significant differences in drought characteristics among different vegetationsof natural vegetation in the Huang-Huai-Hai River Basin. Natural vegetation ecosystem has strongresistance to outside interference, even typical drought year of NDVI substantial change will nothappen. However, different vegetations match different drought tolerance, drought resistant treesis strong, and then shrub and grass is minimum scaling in drought sensitive month. |
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