Temporal divergence in cropping pattern and its implications on geospatial drought assessment

Time series data on cropping pattern at disaggregated level were analysed and its implications on geospatial drought assessment were demonstrated. An index of Cropping Pattern Dissimilarity (CP-DI) between a pair of years, developed in this study, proved that the cropping pattern of a year has a higher degree of similarity with that of recent past years only and tends to be dissimilar with longer time difference. The temporal divergence in cropping pattern has direct implications on geospatial approach of drought assessment, in which, time series NDVI data are compared for drought interpretation. It was found that, seasonal NDVI profiles of drought year and normal year did not show any anomaly when the cropping patterns were dissimilar and two normal years having dissimilar cropping pattern showed different NDVI profiles. Therefore, it is suggested that such temporal comparisons of NDVI are better restricted to recent past years to achieve more objective interpretation.     

Using geographically weighted regression kriging for crop yield mapping in West Africa

Geographical information systems support the application of statistical techniques to map spatially referenced crop data. To do this in the optimal way, errors and uncertainties have to be minimized that are often associated with operations on the data. This paper applies a spatial statistical approach to upscale crop yields from the field level toward the scale of Burkina Faso. Observed yields were related to the Normalized Difference Vegetation Index derived from SPOT-VEGETATION. The objective was to quantify the uncertainties at the subsequent steps. First, we applied a point pattern analysis to examine uncertainties due to the sampling network of field surveys in the country. Second, geographically weighted regression kriging (GWRK) was applied to upscale the yield observations and to quantify the corresponding uncertainty. The proposed method was demonstrated with the mapping of sorghum yields in Burkina Faso and results were compared with those from regression kriging (RK) and kriging with external drift using a local kriging neighborhood (KEDLN). The proposed method was validated with independent yield observations obtained from field surveys. We observed that the lower uncertainty range value increased by 39%, and the upper uncertainty range value decreased by 51%, when comparing GWRK with RK and KEDLN. Moreover, GWRK reduced the prediction error variance as compared to RK (20 vs. 31) and to KEDLN (20 vs. 39). We found that climate and topography had a major impact on the country’s sorghum yields. Further, the financial ability of farmers influenced the crop management and, thus, the sorghum crop yields. We concluded that GWRK effectively utilized information present in the covariate datasets and improved the accuracies of both the regional-scale mapping of sorghum yields and was able to quantify the associated uncertainty.     

Spatial distribution and morphologic characteristics of gullies in the Black Soil Region of Northeast China: Hebei watershed

Gully erosion in the Black Soil Region of China has posed a threat to food security. This study aimed to determine the spatial distribution and morphologic characteristics of gullies in the region and their topographic thresholds. A 28 km² watershed was surveyed and 117 gullies measured. The results showed that: (1) Gullies were distributed equally on both hillslope and valley floor positions, with a total gully density of .66 km/km². (2) The mean depth, width, and cross-sectional area of gullies were .74 m, 2.39 m, and 2.43 m², respectively. These characteristics varied among gullies according to their topographic positions and slope gradients. Individual gully volume (V) was well predicted from gully length (L) by V = 2.08L^0.96 (r² = .66). Total gully volume (V) of each sub-watershed was predicted from mean slope gradient (S) and drainage area (A) as V = 275800S ? 8600A (r² = .73). (3) Gully erosion was more serious in steeper sub-watersheds and steeper hillslope positions. Gullies were wider in regions with relatively larger drainage areas, except for those developed in the main valley. The topographic threshold for gully initiation was S = .10A^?0.34, which indicated gully erosion was dominated by surface runoff. (4) Human activities, such as road construction, played a significant role in gully erosion.     

Ecology of macrozoobenthic communities in two plateau lakes of Southwest China

Ecological studies on macrozoobenthos were conducted in two small plateau lakes in the Yunnan-Guizhou Plateau, Southwest China： Xingyun Lake （XL）, a eutrophic lake whose main source of primary production was phytoplankton （Chl α=99.76±24.01 μg/L）, and Yangzong Lake （YL）, a mesotrophic lake. Sampling was carried out from October 2002 to May 2004. Altogether 23 benthic taxa were identified in XL and 21 taxa in YL. The density of benthos in XL was much lower than that in YL, but the biomass was about equal in the two lakes, being I 423 ind/m^2 and 8.71 g/m^2 in XL and 4 249 ind/m^2 and 8.60 g/m^2 in YL. The dominant species were Limnodrilus hoffmeisteri, Branchiura sowerbyi, Aulodrilus pluriseta and Chironomus sp. in XL and Limnodrilus hoffrneisteri, Aulodrilus pluriseta and Bellamya sp. in YL. Seasonal fluctuation occurred, showing richer species in summer and winter, but the density and biomass varied in different ways in the two lakes. Analyses on functional feeding groups indicate that collector-gatherers were predominant, but the relative abundances of other groups were different. Stepwise multiple regression analysis demonstrated that the water depth, conductivity and chlorophyll a were the key factors affecting macrozoobenthic abundance in the lakes.     

基于WOFOST模型与UAV数据的玉米生长后期地上生物量估算

地上生物量能够有效反映作物的生长状态,其信息的实时估算对产量预测和农田生产管理都有重要意义。作物生长模型因其详尽的生理生化基础和对生长过程数字化描述能力,成为生物量估算的理想模型。近年来,研究人员利用数据同化算法将时间序列遥感数据同化到作物生长模型中,实现了作物模型由基于气象站的点模拟到区域尺度面模拟的外推,使生物量模拟结果同时具备大范围和机理性两个方面的特点。这一模式下,时间序列的遥感数据质量将对生物量模拟精度产生直接影响,作物生长后期受到光谱饱和的影响,遥感数据的作物冠层信息获取能力会出现明显下降,因此有必要对该阶段遥感数据和作物模型的结合方式进行优化,提升生物量模拟精度。本文针对东北地区春玉米生物量遥感估算存在的问题,提出了利用WOFOST作物模型结合无人机（UAV）遥感数据实现作物生长后期生物量准确估算的新思路。新思路首先利用多光谱遥感数据获取WOFOST模型具备较高空间异质性的土壤速效养分参数以提升模型的空间信息模拟能力,使其能在一定程度上摆脱点尺度模拟的限制。同时,结合集合卡尔曼滤波算法将生长前期无人机（UAV）遥感数据同化到模型中,以缩短模型单独运行时间,减少模型运行过程中的参数误差累积,实现无遥感数据参与下的短期作物生长模拟,并输出生长后期相应的生物量模拟结果。最后,本文利用地面实测数据对新方法的生物量模拟精度进行了评价。结果表明,与全生育期数据同化相比,新方法的生物量估算精度有了明显的提升（全生育期同化：R² = 0.45,RMSE = 4254.30 kg/ha;新方法：R²= 0.86,RMSE = 2216.79 kg/ha）。     

Makkink's equation for evapotranspiration applied to unstressed maize

The crop factor method is applied to unstressed maize, in which grass is the reference crop, and the evapotranspiration of the latter is determined with the simplified equation of Makkink as proposed by De Bruin (1987). Using the crop factor published by Feddes (1987), a good agreement is found with measurements collected during the growing season of 1985 at the Sinderhoeve (51° 59′ N, 5° 45′ E) near Renkum in The Netherlands. It appears that Makkink's method yields slightly better results than the Penman–Monteith equation using surface resistances fitted to the data set itself. © 1998 John Wiley & Sons, Ltd.     

Images difference of ASAR data for rice crop mapping in Fuzhou,China

This paper introduces ENVISAT ASAR data application on rice field mapping in the Fuzhou area, using multi-temporal ASAR dual polarization data acquired in 2005. The procedure for ASAR data processing here includes data calibration, image registration, speckle reduction and conversion of data format from amplitude to dB for backscatter. The backscatter of rice increases with the rice growing stages, which was much different from other land covers. Based on image difference techniques, 6 schemes were designed with ASAR different temporal and polarization data for rice field mapping. Difference images between images in the early period of rice crop and growing or ripening period, are more suitable for rice extraction than those difference images between different polarizations in the same date. The most accurate result of late rice extraction was achieved based on the difference of HH polarization data acquired in October and August. Therefore, for rice field mapping, the temporal information is more important than polarization information. The data during the early growing season of rice is very important for high accuracy rice mapping.     

典型岩溶断陷盆地农作物生态需水研究——以蒙自地区为例

从合理调控生态用水角度出发,探讨典型岩溶断陷盆地区农作物生态需水问题。根据蒙自断陷盆地的岩溶地貌特征,分别选取位于盆地、坡面和高原面的大洼子、朵古、牛耳坡3个观测点,利用Penman-Monteith公式、作物系数（FAO推荐）及同期有效降雨量,估算3个观测点2018年的参考蒸散量、生态需水量以及不同作物生长所需的人工灌溉水量。结果表明:（1）大洼子、朵古及牛耳坡的参考蒸散量分别为1 346.10 mm、1 200.00 mm、1 064.30 mm,远大于同期降水量,均呈现出蒸发旺盛的特点,加大了作物对于水分的需求;同时三者的参考蒸散量表现出较为明显的时空差异,使得3个观测点的农业种植条件存在差异;（2）大洼子种植的水稻、小麦、花生、油菜、大豆、马铃薯、葡萄等作物的生态需水定额均远大于大洼子同期的有效降水,在大洼子种植的作物均需要大量人工浇灌才能正常生长,而农作物的种植与其种植条件匹配度不高;（3）朵古及牛耳坡种植的玉米、万寿菊的生态需水定额与同期有效降水之间的差值较小甚至完全满足,表明玉米、万寿菊在高原山区的种植是与当地种植条件相匹配的;而种植在朵古及牛耳坡的苹果、烤烟的生态需水定额与同期有效降水之间的差值较大,表明在高原山区大量种植苹果及烤烟对于人工浇灌要求较高;（4）研究区大部分农作物在生长发育阶段内所需的水分主要依靠人工灌溉,与本地降水分布规律匹配度不高,区内农业结构与种植模式有待调整。在岩溶断陷盆地内要种植耗水较少,对热量要求较高的作物,山区则需要发展具有生态保护和经济效益的作物,但种植的重点区域仍是盆地区。