The role of sampling strategy on apparent temporal stability of soil moisture under subtropical hydroclimatic conditions
The role of sampling strategy on apparent temporal stability of soil moisture under subtropical hydroclimatic conditions
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亚热带水文气候条件下采样策略对土壤湿度表观稳定性的作用
DOI：
10.2478/johh-2019-0006
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发表时间：
2019-09
影响因子：
1.9
通讯作者：
Xinhua Peng
中科院分区：
文献类型：
--
作者：
Lei Gao;Yaji Wang;Xinhua Peng
摘要亚热带地区土壤粘粒丰富，风化程度高，干旱时间长，伴随着强烈的降雨，土壤水分和水文特性波动很大。这使时空动力学的预测变得复杂，因为数据集通常以太粗的分辨率收集，而观测往往代表的持续时间太短，无法捕捉到时间稳定性。本研究的目的是进一步了解时间抽样尺度对观测到的SWC时间稳定性特征的作用，以帮助设计最优SWC抽样策略。这侧重于抽样频率和总监测持续时间，因为以前的分析没有同时考虑这两个抽样方面。我们收集了中国东南部红壤地区不同土壤深度和不同作物(花生和柑橘)的相对高分辨率的SWC数据(每两周一次，超过3.5年)。数据集分为三年培训期和六个月评估期。训练期间共得出13个采样频率(间隔15-240天)和8个监测持续时间(3-36个月)，以确定时间稳定性特征和最稳定的位置(MTSL)。利用独立的评价数据对这些MTSL的预测精度进行了检验。结果表明，植被类型确实影响土壤水分的时空格局，柑橘地比花生地表现出更强的时间变异性和更弱的时间稳定性。然而，无论植被类型或土壤深度如何，采样频率和观测持续时间的影响都更为显著。随着采样间隔的增加或监测持续时间的减少，SWC的时间稳定性被普遍高估；当采样间隔从15天增加到240天时，SWC的时间稳定性被高估了不到10%；当持续时间从36个月减少到3个月时，SWC的时间稳定性被高估了40%。我们的结果表明，采样策略和采样间隔和持续时间之间的权衡应侧重于捕捉水文气候条件下的主要变异性。对于副热带条件，我们发现在24个月内每45天采样一次是确保SWC时间稳定性误差小于10%的最小采样策略。
Abstract Subtropical regions have clay-rich, weathered soils, and long dry periods followed by intense rainfall that produces large fluctuations in soil water content (SWC) and hydrological behavior. This complicates predictions of spatio-temporal dynamics, as datasets are typically collected at too coarse resolution and observations often represent a duration that is too short to capture temporal stability. The aim of the present study was to gain further insights into the role of temporal sampling scale on the observed temporal stability features of SWC order to aid the design of optimal SWC sampling strategies. This focused on both sampling frequency and total monitoring duration, as previous analyses have not considered both of these sampling aspects simultaneously. We collected relatively high resolution data of SWC (fortnightly over 3.5 years) for various soil depths and under contrasting crops (peanuts and citrus) at the red soil region of southeast China. The dataset was split into a three-year training period and a six-month evaluation period. Altogether 13 sampling frequencies (intervals ranging from 15 to 240 days) and eight monitoring duration periods (between three and 36 months) were derived from the training period to identify temporal stability features and the most time stable location (MTSL). The prediction accuracies of these MTSLs were tested using the independent evaluation data. Results showed that vegetation type did affect the spatio-temporal patterns of SWC, whereby the citrus site exhibited a stronger temporal variation and weaker temporal stability than the peanut site. However, the effects of both sampling frequency and observation duration were more pronounced, irrespective of the role of vegetation type or soil depth. With increasing sampling interval or decreasing monitoring duration, temporal stability of SWC was generally overestimated; by less than 10% when sampling interval increased from every 15 to 240 days and by up to 40% with duration decreasing from 36 to 3 months. Our results suggest that sampling strategies and trade-offs between sampling interval and duration should focus on capturing the main variability in hydro-climatological conditions. For subtropical conditions, we found that sampling once every 45 days over 24 months to be the minimum sampling strategy to ensure errors in SWC temporal stability of less than 10%.
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