sustainability Article Lake Area Analysis Using Exponential Smoothing Model and Long Time-Series Landsat Images in Wuhan, China Gonghao Duan 1,* ID and Ruiqing Niu 2 1 Faculty of Information Engineering, China University of Geosciences, Wuhan 430074, China 2 College of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074, China; [email protected] * Correspondence: [email protected] Received: 14 November 2017; Accepted: 8 January 2018; Published: 9 January 2018 Abstract: The loss of lake area significantly influences the climate change in a region, and this loss represents a serious and unavoidable challenge to maintaining ecological sustainability under the circumstances of lakes that are being filled. Therefore, mapping and forecasting changes in the lake is critical for protecting the environment and mitigating ecological problems in the urban district. We created an accessible map displaying area changes for 82 lakes in the Wuhan city using remote sensing data in conjunction with visual interpretation by combining field data with Landsat 2/5/7/8 Thematic Mapper (TM) time-series images for the period 1987–2013. In addition, we applied a quadratic exponential smoothing model to forecast lake area changes in Wuhan city. The map provides, for the first time, estimates of lake development in Wuhan using data required for local-scale studies. The model predicted a lake area reduction of 18.494 km2 in 2015. The average error reached 0.23 with a correlation coefficient of 0.98, indicating that the model is reliable. The paper provided a numerical analysis and forecasting method to provide a better understanding of lake area changes. The modeling and mapping results can help assess aquatic habitat suitability and property planning for Wuhan lakes. Keywords: lake; forecasting; mapping; quadratic exponential 1. Introduction With the development of remote sensing technology, increasingly large data sets of imagery have been used for water resource assessment [1,2]. The Hubei Province is known as “the province of a thousand lakes” in China, as there are more than 80 shallow lakes densely distributed throughout the Wuhan development area alone. The loss of lakes significantly influences the level of environmental pollution as well as climate change in a region, and this loss represents a serious and unavoidable challenge to maintaining ecological sustainability under the circumstances of lakes that are being filled. Therefore, mapping changes in lake areas is critical for protecting the environment and mitigating ecological problems in the Wuhan urban area. Several mapping water studies have been conducted for different research fields. They noted the importance of wetlands for urban landscape planning and delineated the relationship between human health and urban wetland environmental ecosystems [3,4]. Researchers quantified the changes in both lake areas and boundaries from multiple sets of remote sensing images [5,6]. Satellite remote sensing plays a significant role in water resource surveying, hydrological monitoring, wetland protection, and geological disaster warning systems because of the periodic repetition of data and the ability to cover a large area [7–10]. Experts obtained the modified normalized difference water index (MNDWI) by analyzing the differences in the amounts of radiation received from water bodies Sustainability 2018, 10, 149; doi:10.3390/su10010149 www.mdpi.com/journal/sustainability SustainabilitySustainability 20182018,, 1010,, 149149 2 of 16 normalized difference water index (MNDWI) by analyzing the differences in the amounts of andradiation non-water received features from [ 11water]. Some bodies experts and madenon-water a comparative features [11]. study Some of automated experts made water a classificationcomparative methodsstudy of automated [12] and used water moderate-resolution classification methods sensor [12] imagery, and used such moderate-resolution as that acquired from sensor the imagery, Landsat Thematicsuch as that Mapper acquired (TM) from and the Moderate Landsat Themat Resolutionic Mapper Imaging (TM) Spectroradiometer and Moderate Resolution (MODIS) Imaging sensors, toSpectroradiometer obtain the distributions (MODIS) of desiredsensors, features to obtain among the distributions various study of areas desired [13– 15features]. 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Furthermore, information we of provide lake surfaces a valid exponential between model1987 and to forecast 2013. futureFurthermore, changes. we The provide set of a measures valid exponential used herein model includes to forecast the degree future of changes. model fit, The the set robustness of measures of theused model, herein and includes the prediction the degree skill of [26model–29]. fit, Finally, the robustness we map the of changes the model, in lake and area the throughoutprediction skill the Wuhan[26–29]. urban Finally, development we map the district changes (1987–2013), in lake area the throughout results of the which Wuhan are readily urban explainabledevelopment and district may possess(1987–2013), practical the results applications. of which are readily explainable and may possess practical applications. 2. Study Area The city of Wuhan isis locatedlocated toto thethe easteast ofof JianghanJianghan PlainPlain andand isis situatedsituated inin thethe middle of China 2 withwith aa totaltotal areaarea ofof 8494.418494.41 kmkm2.. The The city city is divided into three parts by twotwo majormajor riversrivers thatthat cutcut throughthrough thethe city city centre: centre: the the Yangtze Yangtze River, River, which which is the is third the largestthird largest river in river the world in the and world the Hanjiang and the RiverHanjiang (the River Yangtze (the River’s Yangtze largest River’s tributary). largest tributar The collectivey). The collective water surface water of surface the two of rivers, the two covering rivers, 2 upcovering to 2217.6 up kmto 2217.6, accounts km2, for accounts nearly afor quarter nearly of a thequarter urban of distinct, the urban which distinct, is the which highest is among the highest all of China’samong all major of China’s cities (Figure major 1citiesa). (Figure 1a). (a) (b) Figure 1. 1.( a()a) represents represents the the newest newest Wuhan Wuhan urban urban boundary boundary shapeshape filefile thatthat wewe employemploy toto covercover thethe Landsat 88 remoteremote sensingsensing image image (2013); (2013); (b ()b shows) shows a relativelya relatively scattered scattered distribution distribution of lakes,of lakes, which which are mainlyare mainly concentrated concentrated within within central central and and southern southern Wuhan. Wuhan. The The lakes lakes are are more morelikely likely toto appearappear in low-lyinglow-lying areas with higher elevations, and many small lakes are are developed around around the the main main river. river. TheThe twotwo largestlargest urbanurban lakes lakes (East (East Lake Lake and and Tangxun Tangxun Lake) Lake) are are located located in thein the middle-west middle-west section section of the of studythe study area. area. This This lake distributionlake distribution shows shows that there that arethere abundant are abundant water resourceswater resources in the urban in the area. urban area. As of 2015, there were approximately 166 lakes in Wuhan, which is known as the “city of the As of 2015, there were approximately 166 lakes in Wuhan, which is known as the “city of the hundred lakes”. The lake surface area was 803.17 km2 at normal water level. Tangxun Lake (47.6 km2) hundred lakes”. The lake surface area was 803.17 km2 at normal water level. Tangxun Lake (47.6 is the largest city-lake in China at present [30]. Many large lakes are situated on either side of the two km2) is the largest city-lake in China at present [30]. Many large lakes are situated on either side of main rivers, forming a network of lakes (Figure1b). Our research team conducted a thorough study of the two main rivers, forming a network of lakes (Figure 1b). Our research team conducted a the 82 main lakes in the Wuhan urban area by means of follow-up methods. thorough study of the 82 main lakes in the Wuhan urban area by means of follow-up methods. Sustainability 2018, 10, 149 3 of 16 Sustainability 2018, 10, 149 3 of 16 In our research, we focus on annual changes in the body of the main lakes (1987–2013). In our research, we focus on annual changes in the body of the main lakes (1987–2013). The Theinformation information of ofthe the lake lake boundaries