Answer & Explanation:Hi,I have two more of those scientific journal articles for review that I was wondering if you’d be able to assist me with. Thank you in advance. Both don’t have to be completed by Friday, only one does. I will send you a request for the other later today.you are to pick an ecology article published in an ecology journal
or science journal and you are to review the article just like someone would
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hypothetical audience will be other well-educated scientists.No page limit, but has to be double spaced. Preferable 5 pages.
discuss the following: What was the
article about? What was the hypothesis examined by the researchers (if
there
was one)? How did they conduct their research? What were their results
and
conclusions? Provide your own critical analysis of the positive and
negative aspects of the article, Did you like the article and did you
agree with the authors’
conclusions? Are the conclusions derived logically from the
data/evidence
presented? How effective was the article in communicating its main idea?
What
problems were left unsolved? What possibilities does the article suggest
for
future research?5) BONUS:
Did you use other references to back-up your arguments? This is not
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wej12096.pdf
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Water and Environment Journal. Print ISSN 1747-6585
Impacts of climate and land-cover changes on water resources
in a humid subtropical watershed: a case study from East
Texas, USA
Joonghyeok Heo1, Jaehyung Yu2, John R. Giardino3 & Huidae Cho4
1
Department of Geology & Geophysics, Texas A&M University, College Station, TX, USA; 2Department of Geology and Earth Environmental Science,
Chungnam National University, Daejeon, South Korea; 3Department of Geology & Geophysics and Water Management and Hydrological Science Program,
Texas A&M University, College Station, TX, USA; and 4Water Resources Engineer, Dewberry, Atlanta, GA, USA
Keywords
climate change; humid subtropical watershed;
land cover; water resources.
Correspondence
Jaehyung Yu, Department of Geology and Earth
Environmental Science, Chungnam National
University, Daejeon 305-764, South Korea.
Email: jaeyu@cnu.ac.kr
doi:10.1111/wej.12096
Abstract
This study investigates the response of water resources regarding the climate and
land-cover changes in a humid subtropical watershed during the period 1970–2009.
A 0.7°C increase in temperature and a 16.3% increase in precipitation were
observed. Temperature had a lower increase trend, and precipitation showed definite increasing trend compared to previous studies. The main trend of land-cover
change was conversion of vegetation and barren lands to developed and crop lands
affected by human intervention, and forest and grass to bush/shrub which considered to be caused by natural climate system. Hydrologic responses to climate and
land-cover changes resulted in increases of surface run-off (15.0%), soil water
content (2.7%), evapotranspiration (20.1%) and a decrease in groundwater discharge
(9.2%). We found that surface run-off is relatively stable with precipitation, whereas
groundwater discharge and soil water content are sensitive to changes in land
cover, especially land cover brought about by human intervention.
Introduction
Water is the most important resources for life on Earth. Water
resources are becoming increasingly important because of
current and potential future impacts of climate change, constantly changing land-cover change, increasing population
growth and economic development (IPCC 2007). As a result
of these dynamic changes, many countries around the world
face serious problems with their water supplies.
Climate change is driven by variations in precipitation and
temperature, which can impact streamflow, run-off and
groundwater, all leading to alteration of the hydrological
cycle (Pang et al. 2012). On the other hand, land-cover
changes and human activity can alter the regional hydrologic
cycle by changing surface permeability, soil moisture, run-off,
decreases in vegetation cover and evapotranspiration (Xu
et al. 2010). Thus, climate change, in general, has a direct
impact on the global distribution of water resources, whereas
land-cover change mainly controls local, surface hydrological
processes, which can also impact water resources.
Humid climate is one of the five main climate types in the
Koppen climate classification and can be more classified as
Water and Environment Journal 29 (2015) 51–60 © 2014 CIWEM.
humid subtropical, oceanic and Mediterranean climate (Peel
et al. 2007). Humid climates occupy ∼16% of the land surface
of Earth in terms of area and is mainly located in eastern Asia,
the southern parts of South America, the southeastern part
of North America and the east coast of Australia. Additionally,
a significant amount of the population of the world resides in
this climate zone (Kottek et al. 2006). Fraedrich et al. (2001)
showed that the area of humid climate increased by 2.5% in
North America from 1951 to 2000. They also concluded that
the spatial distribution of humid climates will increase by the
2050s because of climate change.
To clearly understand the impact of climate change solely
on water resources, the impact of land-cover change caused
by human impact has to be discounted (i.e. removed from a
study). Although previous studies (Fitzgerald & Walsh 1987;
Ma et al. 2009; Viger et al. 2011; Candela et al. 2012) have
made advances understanding the impact of climate change
on water resources, no studies clearly focused on the impact
of natural climate change (i.e. no anthropogenic intervention)
on water resources in humid subtropical climates because of
utilising one representative land-cover data for the long-term
observation and including high proportions of urbanised
51
East Texas climate impact
J. Heo et al.
area lies within Hydrologic Unit Code (HUC) 12020006 and
extends into Polk, Tyler, and Hardin counties in Texas. The
land cover of the study area consists mostly of vegetation,
bare soil and water. Because natural areas (i.e. vegetation,
bare soil and water) account for over 95.8% of the total area,
the study area was selected to evaluate the impact of climate
on water resources where human impact is minimal (< 4%).
The climate of the study area is predominantly a humid
subtropical climate with an annual mean temperature of
19.1°C and an annual total precipitation of 1422.1 mm, based
on the 1970–2009 data of the four climatic stations (Fig. 1). A
long period of weather data with a relatively dense meteorological and hydrological observation network is available for
the study area. Because of its relatively natural areas characteristics and availability of quality weather data, the study
area was used to investigate the impact of climate and landcover changes on water resources in a humid subtropical
climate.
Materials and methods
Data
Fig. 1. Location map of the study area.
area. Therefore, natural variations and human interventions
in the land-cover changes were not appropriately considered
in previous assessment.
We selected a watershed with sparse human habitation to
factor out human interaction for a humid subtropical watershed. Three land-cover data, representing subperiods of the
study period, are employed for the water resources assessment to obtain a more realistic estimation of impact. The
impact of climate and land-cover changes on water resources
can be better defined with the most realistic hydrological
model rather than simply observing one representative landcover type. The objectives of this study are (1) to assess the
climate change in a humid subtropical watershed; (2) to identify and explain the types of the changes in land cover; and (3)
to evaluate the impact of climate and land-cover changes on
water resources in the study area. This study provides important information that is of utmost importance for water
resources management of a humid subtropical climate.
Precipitation and temperature data were obtained from the
National Oceanic and Atmospheric Administration (NOAA)
and United States Department of Agriculture (USDA). Daily
temperature and precipitation data from 1970 to 2009 were
used as the basic meteorological input data. Stream discharge
data for the gauge station (08041500) was obtained from the
National Water Information System (NWIS) of the US Geological Survey (USGS). The State Soil Geographic database
(STATSGO) was utilised, which was created in 1994 by the
Natural Resources Conservation Service (NRCS). A 30 m-resolution Digital Elevation Model (DEM) was obtained from Earth
Resource Observation and Sciences (EROS) of the USGS.
The land-cover data sets were generated to simulate three
separate periods for the study area in the Soil and Water
Assessment Tool (SWAT) models. The three temporal periods
represent: 1970–1989, 1990–1999 and 2000–2009. Land Use
and Land Cover (LULC) data were completed via manual interpretation of aerial photography from 1970s to 1980s. The
National Land Cover Dataset (NLCD) 1992 was derived from
early 1990s Landsat Thematic Mapper (TM) satellite data.
NLCD2001 is based on Landsat Enhanced Thematic
Mapper+(ETM+) in the early 2000s. NLCD2001 has been
updated in version NLCD2006 using the Landsat ETM+.
SWAT model
Study area
The study area, with an area of 2221 km2, is located in southeastern Texas, USA (Fig. 1). It is a part of the Neches River
Basin, which discharges into the Gulf of Mexico. The study
52
The SWAT is a basin-scale, continuous simulation model
designed to estimate run-off, soil moisture, groundwater discharge and evapotranspiration (Ma et al. 2009). According to
performance rating (Cho & Olivera 2009), Nash-Sutcliffe
Water and Environment Journal 29 (2015) 51–60 © 2014 CIWEM.
J. Heo et al.
East Texas climate impact
Table 1 Summary for the three models of the Soil and Water Assessment
Tool and the calibration values
Simulations
Years
Land-cover data
NSE
R2
Period 1
Period 2
Period 3
1970–1989
1990–1999
2000–2009
LULC (1970s–1980s)
NLCD1992
NLCD2001
0.74
0.66
0.75
0.79
0.67
0.75
LULC, Land Use and Land Cover; NLCD, National Land Cover Dataset; NSE,
Nash-Sutcliffe Efficiency.
Efficiency (NSE) values greater than 0.75 are very good, and
greater than 0.65 are good. The NSE values of this study
ranged from 0.66 to 0.75 (Table 1), which indicates a good
relationship between simulation and observed data. As mentioned previously, for this study, three SWAT models were
constructed based on three simulation periods (period 1:
1970–1989, period 2: 1990–1999 and period 3: 2000–2009)
with three land-cover data (period 1: LULC, period 2:
NLCD1992 and period 3: NLCD2001) to simulate the most
applicable and accurate hydrological model by applying landcover data representing each period (Table 1). These models
were calibrated using Isolated-Speciation-based Particle
Swarm Optimization, which was successfully applied to stochastic rainfall generation (Cho et al. 2011).
Anomaly analysis shows that temperature increased
0.6°C, and precipitation increased 11.8% in the last 10 years
from the base period of 1970–1999 (Figs 2b and 3b). The
results of anomaly have a low increase in temperature and
definite increase in precipitation, indicating similar patterns
for annual mean temperature and annual total precipitation.
Table 2 shows the trends for temperature and precipitation
for the observation period. The minimum of annual mean
temperature was 17.8°C in period 1, whereas the maximum
of annual mean temperature occurred in period 2 at 20.2°C.
The coefficient of variation for temperature ranged from 0.02
to 0.03; period 3 had the lowest coefficient of variation. This
suggests that period 3 had the smallest variance in annual
mean temperature and shows a relatively even distribution.
The results of significance test show trends in the overall
period which are statistically significant level at 0.05.
However, no significant trends are detected on the subperiod
in the study area. These observation seem reasonable when
considered in the context that global climate has shown different patterns in each of the periods with regard to warming
(1901–1940: greenhouse gas, 1966–2000: El Nino, greenhouse gas) and cooling (1941–1965) (IPCC 2007).
Changes in land cover
Results
Changes in climate
Annual mean temperature shows a slight increasing trend of
0.7°C with a slope of 0.021 for the period 1970–2009
(Fig. 2a). The annual mean temperatures for periods 1, 2 and
3 were 18.8, 19.1 and 19.5°C, respectively (Table 2). Period 1
had a decreasing pattern, and periods 2 and 3 had an increasing pattern. Although the study area experienced a mixed
pattern of decrease and increase in temperature, a slight
increase in temperature occurs over the 40-year period. Previous studies reported increasing patterns of temperature for
humid subtropical climates ranging in increases of 1–2°C
(Fitzgerald & Walsh 1987; Arnell 1992; Candela et al. 2012).
Compared to previous studies, the study area experiences a
lower rate of increase in temperature.
Annual total precipitation increased 16.3% from 1333.7 to
1551.6 mm, for periods 1–3 (Table 2), and the overall trend
shows a relatively higher slope of 7.999 (Fig. 3a). All three
observation periods have increasing patterns, with period 2
showing the highest slope. Previous studies reported a 10%
increase for Severn Valley basin in east Australia (Fitzgerald &
Walsh 1987), a 15% increase for the Wale River basin in England
(Arnell 1992) and a 15% increase for river basins in the north of
Spain (Candela et al. 2012). The magnitude of change in
annual total precipitation in our study area has a higher
increase in precipitation compared to previous studies of
other areas.
Water and Environment Journal 29 (2015) 51–60 © 2014 CIWEM.
Figure 4 shows the historical land-cover maps for the study
area. The areas and percentage of the land-cover types
during the three different time periods are given in Table 3.
The comparison of land-cover change is also applied to
detect the pattern of change in each type of land cover, quantitatively (Table 4).
Changes in land cover from 1970s/1980s to 1990s
Vegetative land cover during the 1970s/1980s makes up
∼95% of the area, and barren land is < 0.7%. Because almost
96% of the area is either natural vegetation or barren land, we
assume that human intervention was minimal (Table 3). In the
1990s, vegetation, barren and crop lands accounted for 94.8,
0.6 and 3.3%, respectively. Compared to the 1970s/1980s, no
major changes occurred in the percentages of developed
land and water. As shown in Table 4(a), 8.1% of grass cover
was converted to crop land, as grass cover decreased from
14.8 to 4.4 km2 during the 20-year period. Moreover, 3.9% of
the forest cover was converted to bush/shrub. Bush/shrub
cover increased from 4.6 to 95.5 km2.
Changes in land cover from 1990s to 2000s
Grass cover decreased from 0.2 to 0.1%, and forest decreased
from 90.3 to 80.6%, whereas bush/shrub cover increased
from 4.3 to 9.1% (Table 3). Total vegetation cover (i.e. the sum
of grass, bush/shrub and forest) decreased from 94.8 to
53
East Texas climate impact
J. Heo et al.
Fig. 2. Temperature change trends; (a) the
temperature and (b) the temperature anomaly
(relative to the 1970–1999).
Table 2 Annual mean temperature and annual total precipitation for the observed periods
Temperature (°C)
Period 1 (1970–1989)
Period 2 (1990–1999)
Period 3 (2000–2009)
Overall
Precipitation (mm)
Mean
MIN
MAX
STD
CV
SIG
Mean
MIN
MAX
STD
CV
SIG
18.8
19.1
19.5
19.1
17.8
18.4
18.9
17.8
19.8
20.2
20.1
20.2
0.6
0.6
0.5
0.6
0.03
0.03
0.02
0.03
0.45
0.27
0.06
0.02
1333.7
1495.3
1551.6
1422.1
944.4
1133.7
1166.2
944.4
2,022.0
1736.0
2067.9
2067.9
292.0
175.8
309.5
280.0
0.22
0.12
0.20
0.20
0.67
1.00
0.90
0.04
MIN, minimum; MAX, maximum; STD, standard deviation; CV, coefficient of variation; SIG: significance test (P-value, trends statistically significant at
P-value < 0.05).
89.8%. However, developed and crop lands increased from
1.1 to 6.3% and from 3.3 to 3.5% in 2000s, respectively.
As shown in Table 4(b), 25.0% of the grass cover was converted to crop land, which indicates human intervention
occurred in the area. Approximately 5.3% of the forest cover
was converted to bush/shrub, and a significant portion (80%)
of barren land was converted to developed land. During the
54
period, the total human intervention occurred to 5.4% of the
study area.
Changes in water resources
The components used in the simulation were surface
run-off, groundwater discharge, soil water content and
Water and Environment Journal 29 (2015) 51–60 © 2014 CIWEM.
J. Heo et al.
East Texas climate impact
Fig. 3. Precipitation change trends; (a) the
precipitation and (b) the precipitation anomaly
(relative to the 1970–1999).
evapotranspiration (Fig. 5 and Table 5). The proportions of
each component to the annual total precipitation are summarised in Table 6. It is important to note that SWAT does not
provide a means to simulate water storage. We calculated
water storage by using the mass balance equation of the
hydrologic cycle.
Surface run-off
Annual total surface run-off for periods 1, 2 and 3 were 221.5,
243.1 and 254.8 mm (Table 5). These values account for 16.4,
16.4 and 16.2% of annual total precipitation for the respective
periods (Table 6). As the values show, the percentage of contribution to the annual total precipitation is relatively stable;
however, surface run-off did increase by 15.0% during the
three periods along with a 16.3% increase in precipitation. It is
Water and Environment Journal 29 (2015) 51–60 © 2014 CIWEM.
interesting to note that although there is a change in temperature and an increasing trend in precipitation, surface runoff remains relatively stable over the time period.
Groundwater discharge
Groundwater discharge shows a decreasing pattern,
whereas annual total precipitation shows an increasing
pattern. Annual total groundwater discharge was 14.1 mm in
period 1, 13.2 mm in period 2 and 12.8 mm in period 3
(Table 5). The contribution to annual total precipitation was
1.0, 0.9 and 0.8% (Table 6). A fact that groundwater discharge
showed a generally decreasing pattern from 1970 to 2009 is
important for the future. This pattern runs counter to the
general conception of a positive relationship between precipitation and groundwater discharge.
55
East Texas climate impact
J. Heo et al.
Fig. 4. Land-cover maps of the study area; (a) LULC, (b) NLCD1992, (c) NLCD2001, and (d) NLCD2006. LULC, Land Use and Land Cover; NLCD, National Land
Cover Dataset.
Table 3 The area for each land-cover type in the study area (unit: km2)
LULC
NLCD1992
NLCD2001
NLCD2006
Changes
G
BS
F
D
B
W
C
Total
14.8 (0.7%)
4.4 (0.2%)
2.7 (0.1%)
2.2 (0.1%)
−12.4 (− 0.6%)
4.6 (0.2%)
95.5 (4.3%)
202.1 (9.1%)
202.1 (9.1%)
197.5 (8.9%)
2087.7 (94.0%)
2005.6 (90.3%)
1790.1 (80.6%)
1790.1 (80.6%)
−297.6 (− 13.4%)
23.8 (1.1%)
24.2 (1.1%)
138.8 (6.3%)
138.8 (6.3%)
115.0 (5.2%)
14.4 (0.7%)
14.0 (0.6%)
2.7 (0.1%)
2.7 (0.1%)
−11.7 (− 0.6%)
4.7 (0.2%)
5.1 (0.2%)
5.8 (0.3%)
5.8 (0.3%)
1.1 (0.1%)
71.0 (3.1%)
72.2 (3.3%)
78.8 (3.5%)
79.3 (3.5%)
8.3 (0.4%)
2221.0 (100.0%)
2221.0 (100.0%)
2221.0 (100.0%)
2221.0 (100.0%)
G, grass; BS, bush/shrub; F, forest; D, developed land; B, barren land; W, water; C, crop land.
56
Water and Environment Journal 29 (2015) 51–60 © 2014 CIWEM.
J. Heo et al.
East Texas climate impact
Table 4 The comparison of land-cover change between the three different time periods; (a) LULC(1970/80s)–NLCD1992 and (b) NLCD1992–NLCD2001
(unit: km2)
NLCD1992
(a)
G
BS
LULC
4.4 (29.7%)
8.8 (59.5%)
4.6 (100.0%)
82.1 (3.9%)
G
BS
F
D
B
W
C
NLCD1992 Total
4.4 (100.0%)
(b)
G
NLCD1992
2.7 (61.4%)
F
D
B
W
0.4 (2.7%)
C
1.2 (8.1%)
5.1 (100.0%)
71.0 (100.0%)
72.2 (100.0%)
14.8 (100.0%)
4.6 (100.0%)
2087.7 (100.0%)
23.8 (100.0%)
14.4 (100.0%)
4.7 (100.0%)
71.0 (100.0%)
2221.0
W
C
NLCD1992 Total
2005.6 (96.1%)
23.8 (100.0%)
0.4 (2.8%)
14.0 (97.2%)
4.7 (100.0%)
95.5 (100.0%)
2005.6 (100.0%)
24.2 (100.0%)
BS
F
D
14.0 (100.0%)
LULC Total
NLCD2001
G
BS
F
D
B
W
C
NLCD2001 Total
0.6 (13.6%)
95.5 (100.0%)
106.6 (5.3%)
2.7 (100.0%)
B
202.1 (100.0%)
1790.1 (89.3%)
1790.1 (100.0%)
103.4 (5.2%)
24.2 (100.0%)
11.2 (80.0%)
2.7 (19.3%)
0.1 (0.7%)
5.1 (100.0%)
138.8 (100.0%)
2.7 (100.0%)
5.8 (100.0%)
1.1 (25.0%)
5.5 (0.2%)
72.2 (100.0%)
78.8 (100.0%)
4.4 (100.0%)
95.5 (100.0%)
2005.6 (100.0%)
24.2 (100.0%)
14.0 (100.0%)
5.1 (100.0%)
72.2 (100.0%)
2221.0
G, grass; BS, bush/shrub; F, forest; D, developed land; B, barren land; W, water; C, crop land; LULC, Land Use and Land Cover; NLCD, National Land Cover
Dataset.
Fig. 5. Annual total amount of surface run-off,
groundwater discharge, soil water content,
and evapotranspiration simulated by the Soil
and Water Assessment Tool.
Table 5 Annual amount of each hydrological component as derived by the Soil and Water Assessment Tool (unit: mm)
Period 1 (1970–1989)
Period 2 (1990–1999)
Period 3 (2000–2009)
Changes
Surface run-off
Groundwater discharge
Soil water conten ...
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