Simulation of regional groundwater levels in arid regions using interpretable machine learning models.

Assessment of influencing factors on non-point source pollution critical source areas in an agricultural watershed

It is highly necessary to apply unmanned aerial vehicle (UAV) remote sensing technology to forest health assessment. To prove the feasibility of quantitative inversion of photosynthetic pigment content (PPC) in Populus euphratica Oliv. individual tree canopy (PeITC) by using multispectral UAV images, in this study, Parrot Sequoia+ multispectral UAV system was manipulated to collect the images of Populus euphratica (Populus euphratica Oliv.) sample plots in Daliyabuyi Oasis from 2019 to 2020, and the canopy PPCs of five Populus euphratica sample trees per plot were determined in six plots. The Populus euphratica crown regions were extracted by grey wolf optimizer-OTSU (GWO-OTSU) multithreshold segmentation algorithm from the normalized difference vegetation index (NDVI) images of Populus euphratica sample plots obtained after preprocessing, and the PeITCs were segmented by multiresolution segmentation algorithm. The mean values of 27 spectral indices in the PeITCs were calculated in each plot, and the optimal model was constructed for quantitative estimation of the PPCs in the PeITCs, then the inversion results were compared and verified based on GF-6 and ZY1-02D satellite imageries respectively. The results were as follows. (1) The average value of canopy chlorophyll content (Chl) was 2.007 mg/g, the mean value of canopy carotenoid content (Car) was 0.703 mg/g. The coefficient of variation (C.V) of both were basically the same and they were both of strong variability. The measured PPCs of the PeITCs in Daliyabuyi Oasis was generally low. The average contents of chlorophyll and carotenoid in PeITC in June were more than twice those in August, while the mean ratio between them was significantly lower in June than in August. The measured PPCs had no obvious spatial distribution law. However, that could prove the rationality of sample selection in this study. (2) NDVI had the best effect of highlighting vegetation among all quadrats in the study area. Based on the GWO-OTSU multithreshold segmentation method, the canopy area of Populus euphratica could be quickly and effectively extracted from the quadrat NDVI map. The best segmentation effect of PeITCs was obtained based on a multiresolution segmentation method when the segmentation scale was 120, the shape index was 0.7, and the compactness index was 0.5. Compared with manual vectorization method of visual interpretation, the root mean square error (RMSE) and Pearson correlation coefficient (R) values of the mean NDVI values in PeITCs obtained by these two methods were 0.038 and 0.951. (3) Only 12 of the 27 spectral indices were significantly correlated with Chl and Car at the significance level of 0.02. Characteristics of the calibration set and validation set were basically consistent with those of the entire set. The classification and regression tree-decision tree (CART-DT) model performed best in the estimation of the PPCs in the PeITCs, in which, when estimating the Car, the calibration coefficient of determination (R2C) was 0.843, the calibration root mean square error (RMSEC) was 0.084, the calibration residual prediction deviation (RPDC) was 2.525, the validation coefficient of determination (R2V) was 0.670, the validation root mean square error (RMSEV) was 0.251, the validation residual prediction deviation (RPDV) was 1.741. (4) Qualitative comparison of spectral reflectance and NDVI values between GF-6 multispectral imagery and Parrot Sequoia+ multispectral image on the 172 PeITCs can show the reliability of Parrot Sequoia+ multispectral image. The comparison results of five PeITCs relative health degree judged by field vision judgment, measured SPAD value, predicted value of Chl (Chlpre), the red edge value calculated by ZY1-02D (ZY1-02Dred edge) and the Carotenoid Reflection Index 2 (CRI2) value calculated by ZY1-02D (ZY1-02DCRI2) can further prove the scientificity of inversion results to a certain extent. These results indicate that multispectral UAV images can be applied for quantitative inversion of PPC in PeITC, which could provide an indicator for the construction of a Populus euphratica individual tree health evaluation indicator system based on UAV remote sensing technology in the next step.

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What Is the Effect of Quantitative Inversion of Photosynthetic Pigment Content in Populus euphratica Oliv. Individual Tree Canopy Based on Multispectral UAV Images?

A framework for identifying priority areas through integrated eco-environmental risk assessment for a holistic watershed management approach

Based on the daily average temperature,maximum and minimum temperature data of 2 weather stations of Dingxin,Ejina Banner in the Heihe River's downstream in 1960~2010,using the methods of climate trending rate and Mann-Kendall abrupt change test method,the characteristics and respond of Populus euphratica's phenology to climate change was analyzed,including beginning dates,ending dates of annual growth period,the annual growth period of P.euphratica and the P.euphratica's beginning dates of yellow leaf stage.The results showed that:(1)The mean annual temperatures in the oasis of lower reaches Heihe River was significantly warming,and the air temperature in the study area which was the oasis of Dingxin and Ejina Banner increased respectively 1.6℃ and 2.4℃ from 1960 to 2010.(2)The change trend of P.euphratica's characteristics was different in recent 51 years.The beginning dates of annual growth of P.euphratica in the lower reaches Heihe River was becoming earlier.The beginning dates of annual growth of P.euphratica in the oasis of Dingxin and Ejina Banner were-1.46 d/10a(α=0.01),-1.54 d/10a(α=0.02),and they were respectively earlier 7 days and 8 days in recent 51 years.The ending dates was becoming later,they were respectively later 5 days and 9 days in recent 51 years,and it was more appreciable in the oasis of Ejina,it was the most significant in 2000s among the change of decades;The growth period of P.euphratica was prolonged,and the trend of P.euphratica's annual growth in the oasis of Ejina was more extended 0.9 d/10a than Dingxin,and the average annual length growth was shorten 1 day;the P.euphratica's beginning dates of yellow leaf stage was becoming slightly later,but it responsed the seasonal change of the climate characteristic in a certain extent,and it was coincided that conclusions which was the temperature changes with temperature fall were not significant.(3)There was significantly different in the abrupt change about P.euphratica phenology,and it was more sensitive in the ending dates.Therefore,it was an obvious response to the climatic change of the P.euphratica in the study area,especially there was more sensitive in Ejina Banner.

Respond of Populus euphratica Oliv.Phenology to Climate Warming in the Oasis of Lower Reaches of Heihe River from 1960 to 2010

Quantifying the phenological variations of Populus euphratica Olivier (P. euphratica) resulting from climate change is vital for desert ecosystems. There has previously been great progress in the influence of climate change on vegetation phenology, but knowledge of the variations in P. euphratica phenology is lacking in extremely arid areas. In this study, a modified method was proposed to explore P. euphratica phenology and its response to climate change using 18-year Global Land Surface Satellite (GLASS) leaf area index (LAI) time series data (2000–2017) in the upper Tarim River basin. The start of the growing season (SOS), length of the growing season (LOS), and end of the growing season (EOS) were obtained with the dynamic threshold method from the reconstructed growth time series curve by using the Savitzky–Golay filtering method. The grey relational analysis (GRA) method was utilized to analyze the influence between the phenology and the key climatic periods and factors. Importantly, we also revealed the positive and negative effects between interannual climate factors and P. euphratica phenology using the canonical correlation analysis (CCA) method, and the interaction between the SOS in spring and EOS in autumn. The results revealed that trends of P. euphratica phenology (i.e., SOS, EOS, and LOS) were not significant during the period from 2000–2017. The spring temperature and sunshine duration (SD) controlled the SOS, and the EOS was mainly affected by the temperature and SD from June–November, although the impacts of average relative humidity (RH) and precipitation (PR) on the SOS and EOS cannot be overlooked. Global warming may lead to SOS advance and EOS delay, and the increase in SD and PR may lead to earlier SOS and later EOS. Runoff was found to be a more key factor for controlling P. euphratica phenology than PR in this region.

Populus euphratica Phenology and Its Response to Climate Change in the Upper Tarim River Basin, NW China

A framework to assess spatio-temporal variations of potential non-point source pollution risk for future land-use planning

Roofs occupy a great proportion of urban impervious surfaces, and the implementation of eco-roof construction in urban areas is beneficial to alleviate the ecological and environmental problems caused by rapid urbanization. In this study, different eco-roofs (i.e., 68.6%-90.7%, and 39.8%-54.5%, respectively. However, all the eco-roofs were sources of NO-3-N, DCr, DFe, and DNi. The blue roof was a sink of DCu (with a pollutant load reduction rate of 21.9%) and did not affect the cumulative load of PO3-4-P in runoff. However, the green roof and blue-green roof were the sources of PO3-4-P and DCu. The RQI value of the blue roof was the highest, followed by that of the blue-green roof and green roof. The RQI value of the green roof was significantly lower than that of the blue and blue-green roofs (P<0.05). These results indicated that the runoff quality of the blue roof was the best, whereas that of the green roof was the worst. Adding a storage layer to the green roofs could significantly improve the runoff quality. The results of this study provide scientific references for the selection and design of eco-roof facilities.

Hualin Li

Papers

Populus euphratica Phenology and Its Response to Climate Change in the Upper Tarim River Basin, NW China

A framework to assess spatio-temporal variations of potential non-point source pollution risk for future land-use planning

A framework for identifying priority areas through integrated eco-environmental risk assessment for a holistic watershed management approach

[Effects of Green, Blue, and Blue-green Roofs on Runoff Quality].

Applicability assessment of five evapotranspiration models based on lysimeter data from a bioretention system