研究生知识库

由于降雨在土壤侵蚀过程中起到的关键性作用，本研究基础长时间尺度的降雨数据，估算了全球1901-2016年降雨侵蚀力，探讨其时空演变特征。鉴于喀斯特地区特殊的地质背景，传统土壤侵蚀估算模型在该地区直接使用会存在一定误差等问题，本研究以中国南方喀斯特槽谷区为研究对象，对其降雨侵蚀力估算方法进行了改进，基于像元尺度估算了槽谷区喀斯特地区不同岩性组合碳酸盐岩的土壤允许流失量，以此对槽谷区土壤侵蚀量进行校正，探讨了该地区2000-2015年土壤侵蚀的时空演变特征并模拟了2020年土壤侵蚀等级状况。结果表明： （1）百年来全球降雨侵蚀力的年均值为3259.21 MJ mm ha?1 h?1 yr?1，且存在高变异性；有超过一半的区域年平均降雨侵蚀力集中在1000 MJ mm ha?1 h?1 yr?1到3000 MJ mm ha?1 h?1 yr?1这个范围。全球降雨侵蚀力的地域差异十分明显，高值区主要集中在东南亚地区、中非地区、南美洲部分地区、中美洲以及加勒比等地。低值区主要分布在西伯利亚、中东地区、北非地区、加拿大以及北欧等地。（2）季降雨侵蚀力的空间分异十分明显。按照北半球的春季(3—5月)、夏季(6—8月)、秋季(9—11月)和冬季(12—1月)对全球降雨侵蚀力的季节变化进行分析，结果表明全球降雨侵蚀力季最大值出现在夏季的东南亚地区、西非地区以及拉丁美洲地区，其降雨侵蚀力量级都在1700 MJ mm ha?1 h?1以上；低值区主要分布在美国中西部、墨西哥大部分地区、南美洲西海岸和东北角、北非的萨赫勒地区和非洲南部、哈萨克斯坦和蒙古国北部、印度西部、中国北方的部分地区、澳大利亚中部沙漠外的大部分地区及沙漠地区。此外，降雨侵蚀力高值区在纬度上表现为以赤道为中心、南北回归线之间波动的周期性变化。（3）百年平均降雨侵蚀力值最高的大洲是南美洲，为5621.86 MJ mm ha?1 h?1 yr-1；最低的是北美洲，为2652.45MJ mm ha?1 h?1 yr-1。以热带雨林气候、热带湿润气候、热带季风气候以及热带草原气候为代表的热带湿润半湿润地区降雨侵蚀力最高，均在4500 MJ mm ha?1 h?1 yr-1以上；而极地气候、冰原气候、冻原气候和亚寒带针叶林气候等寒冷地区以及干旱气候地区降雨侵蚀力最小，均在3000 MJ mm ha?1 h?1 yr-1以下。平原（＜200m）地区百年平均降雨侵蚀力最高，为3475.29 MJ mm ha?1 h?1 yr-1；高山（3500-5000m）以及极高山（＞5000m）地区百年平均降雨侵蚀力最低，均在2700 MJ mm ha?1 h?1 yr-1以下。此外，降雨侵蚀力密度高值区主要集中在干旱区以及部分沿海地区，而低值区主要集中在热带周围。表明降水量很高的地区，其侵蚀密度不一定高。基于像元尺度的降雨侵蚀力变化趋势分析表明全球大部分区域的降雨侵蚀力百年来处于轻微增加和稳定的趋势。 （4）在喀斯特槽谷区，不同岩性组合下碳酸盐岩的土壤允许流失量存在一定差异。其中，连续性碳酸盐岩的土壤允许流失量为0.31 t ha-1 yr-1，碳酸盐岩夹碎屑岩的土壤允许流失量为1.21 t ha-1 yr-1，碳酸盐岩与碎屑岩互层的土壤允许流失量为2.83 t ha-1 yr-1。（5）经过降雨侵蚀力和允许流失量校正后，喀斯特槽谷区年平均土壤侵蚀量为3.08 t ha-1 yr-1，相当于RUSLE模型结果的41.12%，其中喀斯特地区土壤侵蚀量的修正结果仅为RUSLE模型结果的15.63%。也就是说，传统模型在喀斯特地区直接使用，可能导致土壤侵蚀被高估85%左右。（6）当前土壤侵蚀分级标准在喀斯特地区不适用。可以考虑利用理论土壤侵蚀量与土壤允许流失量的比值来反映喀斯特地区土壤侵蚀的风险。既能准确反映该地区水土流失的实际情况，又可以为喀斯特地区的可持续发展提供参考。（7）喀斯特槽谷区2000—2015年土壤侵蚀分布以微度侵蚀为主，侵蚀总量由61.86×107t yr-1减少至2.97×107t yr-1，区域年平均侵蚀模数由21.61t ha-1 yr-1降低至1.04t ha-1 yr-1，侵蚀状况整体在减轻。15年来轻度及轻度以下侵蚀等级的面积增加了76.13×105ha，增幅达36.32%；重度及重度以上侵蚀面积减少了46.90×105ha，降幅达到99.85%。不同地貌类型之间的土壤侵蚀状况存在一定差异，平原地区侵蚀模数最小，盆地地区侵蚀模数最大，达到平原地区侵蚀模数的近四倍。 （8）研究时段内有39.80%的区域土壤侵蚀等级降低，侵蚀程度减弱，仅有0.03%的区域土壤侵蚀等级升高，侵蚀程度加剧， 15年间槽谷区轻度及轻度以上侵蚀等级都逐渐向微度侵蚀等级转移，土壤侵蚀等级由高等级向低等级转移率达到了98%以上，总体呈现出好转的趋势。 （9）基于CA-Markov模型模拟槽谷区土壤侵蚀等级的未来演变趋势，总体Kappa系数达到了0.9788，且各土壤侵蚀等级的系数也在0.65以上，表明预测结果和计算结果的一致性显著，能够较为准确的反映未来槽谷区土壤侵蚀等级的分布状况。到2020年，槽谷区土壤侵蚀等级基本为微度和轻度侵蚀，中度及中度以上侵蚀等级面积仅占研究区面积的0.03%，土壤侵蚀程度继续好转，未来槽谷区土壤侵蚀状况将进一步改善。本研究的结果对于全球降雨侵蚀力以及土壤侵蚀的进一步研究具有一定的参考价值，对于喀斯特生态环境脆弱区土壤侵蚀的准确估算、土壤侵蚀的防治及石漠化治理具有一定的指导意义，对于下一步土壤侵蚀有针对性的防治十分必要。

Due to the key role of rainfall in the process of soil erosion, we estimated the global rainfall erosivity from 1901 to 2016 and explored its temporal and spatial evolution characteristics based on the long-term rainfall data. Moreover, in view of the special geological background of karst area, the soil holding capacity is highly limited, so it is necessary to consider the allowable loss of soil, there may be some errors in the direct use of the traditional soil erosion model in this area. In this study, taking the karst valley area in southern China as the research object, we improved the method of estimating rainfall erosivity, and estimated soil loss tolerance on the pixel scale of different lithologic carbonate rocks in the karst area of the valley area to correct the soil erosion in the valley. Then estimated the soil erosion in valley from 2000 to 2015 to analyze spatio-temporal evolution and predict the soil erosion grade in 2020. Major findings are as follows:(1) The annual mean of global rainfall erosivity over the past one hundred years is 3259.21 MJ mm ha?1 h?1 yr?1 with high variability; over half of the regional average rainfall erosivity is concentrated in the range of 1000 MJ mm ha?1 h?1 yr?1 to 3000 MJ mm ha?1 h?1 yr?1. The geographical differences in global rainfall erosivity are obvious. The high-value areas are mainly concentrated in Southeast Asia, Central Africa, and parts of South America, Central America and the Caribbean. Low-value areas are mainly distributed in Siberia, the Middle East, North Africa, Canada and Northern Europe.(2) The spatial variation of seasonal rainfall erosivity is also obvious. We analyzed the seasonal variations of global rainfall erosivity in spring (March-May), summer (June-August), autumn (September-November) and winter (December-January) in the Northern Hemisphere in this paper. The results show that the maximum rainfall erosivity season occurs in Southeast Asia, West Africa and Latin America in summer, with level more than 1700 MJ mm ha?1 h?1 yr?1, while minimum value areas are mainly distributed in the Midwestern United States, most of Mexico, the west coast of South America and the northeast corner, the Sahel region of North Africa and southern Africa, northern Kazakhstan and northern Mongolia, parts of western India, parts of northern China, most of the desert outside central Australia and desert areas. In addition, the high rainfall erosivity zone appears as a cyclical change in the latitude with the equator as the center and the fluctuation between the Tropics of Cancer and Capricorn.(3) South America had the highest annual average rainfall erosivity (5621.86 MJ mm ha?1 h?1 yr?1), while North America had the lowest (2652.45 MJ mm ha?1 h?1 yr?1). Rainfall Erosivity in tropical humid and semi-humid areas represented by tropical rainforest climate, tropical humid climate, tropical monsoon climate and tropical grassland climate is the highest, all above 4500 MJ mm ha?1 h?1 yr?1, while in cold areas such as polar climate, ice sheet climate, frozen plateau climate, sub-cold zone coniferous forest climate and dry climate areas, rainfall erosivity is the lowest, all below 3000 MJ mm ha?1 h?1 yr?1. The average annual rainfall erosivity in plain (<200m) area is the highest, which is 3475.29 MJ mm ha?1 h?1 yr?1; in alpine (3500-5000m) and extremely alpine (>5000m) areas, the average annual rainfall erosivity is the lowest, which is below 2700 MJ mm ha?1 h?1 yr?1. In addition, the high-value areas of rainfall erosivity density are mainly concentrated in arid areas and some coastal areas, while the low-value areas are mainly concentrated around the tropics. It shows that the erosion density is not necessarily high in areas with high precipitation. The trend analysis of rainfall erosivity based on pixel scale shows that rainfall erosivity in most regions of the world has been slightly increasing and stabilizing over the past one hundred years.(4) In karst valley, the soil loss tolerance for carbonate rock is different under different lithological combinations. The soil loss tolerance of homogenous carbonate rocks (HC) was 0.31 t ha-1 yr-1 with that of carbonate rocks intercalated with clastic rocks (CI) and carbonate/clastic rock alternations (CA) being 1.21 t ha-1 yr-1 and 2.83 t ha-1 yr-1 respectively. (5) After the modification by rainfall erosivity and soil loss tolerance, the average annual magnitude of soil loss in the study area was 3.08 t ha-1 yr-1, which was only 41.12% of that calculated by the initial RUSLE model. The correction result of soil erosion in the karst area is only 15.63% of the RUSLE model. That is to say, the direct use of traditional models in karst areas may lead to the overestimation of soil erosion by about 85%.(6) Current classification criteria for soil erosion are not applicable in karst areas. The ratio of theoretical soil erosion to soil allowable loss can be considered to reflect the risk of soil erosion in karst areas. It can not only accurately reflect the actual situation of soil erosion in the region, but also provide reference for the sustainable development of the karst region.(7) The distribution of soil erosion in karst valley from 2000 to 2015 is mainly micro-erosion. The total amount of soil erosion in karst valley decreased from 61.86×107t yr-1 to 2.97×107t yr-1 from 2000 to 2015, and the annual average erosion modulus of the area reduced from 21.61t ha-1 yr-1 to 1.04t ha-1 yr-1. The overall erosion situation is mitigating. The area of erosion grades in mild and below mild increased by 76.13×105ha, while strong and above strong decreased by 46.90×105ha with the ratio of 99.85%, the erosion situation reduced significantly for 15 years. There are some differences in soil erosion between different geomorphological types. The erosion modulus in plain area is the smallest, while that in basin area is the largest, reaching nearly four times the erosion modulus in the plain.(8) From 2000 to 2015, 39.80% of the regional soil erosion grade decreased and the degree of erosion weakened. Only 0.03% of the soil erosion grades increased and the degree of erosion intensified. During the study period, the mild and above mild erosion levels in the karst valley gradually shifted to the level of micro-erosion, and the rate of soil erosion grade shifted from the high grade to the low grade reached more than 98%, showing a general trend of improvement.(9) We simulated the future evolution trend of the soil erosion grade in the valley in 2020 based on the CA-Markov model. The overall Kappa coefficient reaches 0.9788, and the coefficients of each soil erosion grade are above 0.65. It shows that the predicted results are in good agreement with the calculated results, which can reflect the distribution of soil erosion grade in valley area in the future more accurately. By 2020, the soil erosion level in the trough area will be micro-degree and mild erosion basically, the moderate and moderate erosion grade area only accounts for 0.03% of the study area. The degree of soil erosion will continue to improve, and the situation of soil erosion in valley will be further improved in the future.The results of this study have a certain reference value for the further study of global rainfall erosivity and soil erosion. It has a certain guiding significance for the accurate estimation of soil erosion, the prevention of soil erosion and the control of rocky desertification in the fragile karst ecological environment area. It is also necessary for the next step of the targeted prevention and control of soil erosion.