**5. Land surface temperature analysis**

The MODIS sensor, onboard Terra and Aqua polar satellites, provides one day and one night image under clear sky conditions. MODIS is particularly suitable for the land sur‐ face temperature (LST) product due to its global coverage, radiometric resolution and dy‐ namic ranges for a variety of land cover types and high calibration accuracy in multiple thermal bands.

MODIS LST product is based on the generalized split-window (GSW) algorithm (Wan & Dozier, 1996) using as input the MODIS thermal bands 31 and 32. The parameters in the MODIS GSW depend on the satellite zenith view angles, column water vapor and also on the low atmosphere boundary temperature. The band emissivities rely on the classificationbased method (Snyder et al., 1998) according to land cover types in the pixel (Monteiro et al., 2007). Temperatures are extracted in Kelvin; accuracy of 1 Kelvin is yielded for materials with known emissivities (Wan, 1999), while a number of studies have also tested the accura‐ cy of the MODIS LST product with favorable results (Wan, 2002; Wan et al., 2004; Coll et al., 2005; Wan, 2008).

The MODIS Aqua product MYD11A1 (V5) and MODIS Terra product MOD11A1 (V5) – Land Surface Temperature and Emissivity Daily L3 Global 1 km Grid SIN were used. Terra and Aqua overpass times for the study area are considered at approximately 1030 and 1330 UTC for day passes, and at approximately 2230 and 0130 UTC for night passes, respectively.

The use of MODIS LST data for examining the temporal evolution and the retrieved temper‐ ature anomaly maps for a heat wave event occurred on 24 June 2007 is presented. Moreover, MODIS LST data are used for calculating the urban heat island (UHI) at four urban areas of Cyprus during the extreme heat wave of August 2010.

#### **5.1. MODIS LST temporal evolution and temperature anomaly maps**

**Figure 9.** Neural network performance for the Training, Validation, Test and All data sets

12 Remote Sensing of Environment: Integrated Approaches

MODIS LST data were initially used for generating mean monthly climatology LST maps for June in the period of 2003-2008. The mean and maximum Aqua day and night LST values for June are presented in Fig. 10 for the period 2003-2008 for two urban areas (Nicosia, Lar‐ naca) and one rural area (Ag. Marina). The curves show that the mean night LST values for the two urban areas are similar, while for the area of Ag. Marina, the temperature levels are 3-4 °C lower. For all sites, a minimum was observed for year 2005. The situation is different though regarding day LST values. The coastal site of Larnaca exhibited the lowest values among the three areas, while Nicosia and Ag. Marina exhibited similar patterns and temper‐ ature levels. The overall trend over time for the three areas showed a positive trend.

The intense heat wave event of 24 June 2007 was next examined in order to study the LST behavior during such events since satellite derived LST is controlled by land cover and topographic effect factors. In Fig.11, temperature anomaly maps, in terms of temper‐ ature deviation from the long-term monthly mean values (calculated for the period 2003-2008), are presented for the heat wave event under consideration and for both night and day Aqua passes.

The spatial patterns observed in the temperature anomaly maps are complex. It can be ob‐ served that day LST anomaly is more intense (up to 15°C) than the night anomaly. Mini‐ mum anomaly is located in the area of the mountain range Troodos (central-eastern part), while the southern part of Cyprus presents higher anomaly values than the northern part. The different values of LST increase are attributed to the difference in the emitted radiance from each land type and/or the urban heat island effect.

**Figure 10.** Yearly evolution of the mean Aqua MODIS LST for June (2003-2008) as retrieved from Aqua satellite for three different areas in Cyprus

The amplitude of LST anomaly variation between day and night was examined with the land cover types based on the CORINE 2000 land cover map (Fig. 12). It was found that the mean anomaly amplitude was 2.89-4.05°C for artificial surfaces, 2.87-6.01°C for agricultural areas and 2.81-4.63°C for forest and semi natural areas. However, variations were noticed even in the same category. For example, for artificial surfaces the higher amplitude was no‐ ticed for airports and the lower for dump sites. For agricultural areas, the higher amplitude was noticed for pastures and the lower for annual crops associated with permanent crops. For forest and semi natural areas, the higher amplitude was noticed for beaches, dunes and sands and the lower for mixed forest.

A close inspection on the Aqua LST image (Fig. 12) acquired on 24 June 2007 (day pass) de‐ picted that the highest LST values are noticed in areas that are recognized as vulnerable to desertification (Fig. 13). In Cyprus, there are two climatic zones that are considered as sensi‐ tive to desertification: the semi-arid, which extends over the larger part of the island and the arid sub-humid, which covers the slopes of the Troodos range and the windward side and higher parts of the Kyrenia range (IACO, 2007).

**Figure 11.** Land Surface Temperature anomaly map derived from both day (top) and night (bottom) Aqua MODIS

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passes for the selected heat wave event

The spatial patterns observed in the temperature anomaly maps are complex. It can be ob‐ served that day LST anomaly is more intense (up to 15°C) than the night anomaly. Mini‐ mum anomaly is located in the area of the mountain range Troodos (central-eastern part), while the southern part of Cyprus presents higher anomaly values than the northern part. The different values of LST increase are attributed to the difference in the emitted radiance

**Figure 10.** Yearly evolution of the mean Aqua MODIS LST for June (2003-2008) as retrieved from Aqua satellite for

The amplitude of LST anomaly variation between day and night was examined with the land cover types based on the CORINE 2000 land cover map (Fig. 12). It was found that the mean anomaly amplitude was 2.89-4.05°C for artificial surfaces, 2.87-6.01°C for agricultural areas and 2.81-4.63°C for forest and semi natural areas. However, variations were noticed even in the same category. For example, for artificial surfaces the higher amplitude was no‐ ticed for airports and the lower for dump sites. For agricultural areas, the higher amplitude was noticed for pastures and the lower for annual crops associated with permanent crops. For forest and semi natural areas, the higher amplitude was noticed for beaches, dunes and

A close inspection on the Aqua LST image (Fig. 12) acquired on 24 June 2007 (day pass) de‐ picted that the highest LST values are noticed in areas that are recognized as vulnerable to desertification (Fig. 13). In Cyprus, there are two climatic zones that are considered as sensi‐ tive to desertification: the semi-arid, which extends over the larger part of the island and the arid sub-humid, which covers the slopes of the Troodos range and the windward side and

from each land type and/or the urban heat island effect.

14 Remote Sensing of Environment: Integrated Approaches

three different areas in Cyprus

sands and the lower for mixed forest.

higher parts of the Kyrenia range (IACO, 2007).

**Figure 11.** Land Surface Temperature anomaly map derived from both day (top) and night (bottom) Aqua MODIS passes for the selected heat wave event

lection of the MODIS Aqua data was based on the criterion that the night-time acquired im‐ ages allow a more precise LST calculation since there is no incoming solar radiation to change the surface radiation balance, while night-time MODIS LST accuracy has been found

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**Figure 14.** Areas sensitive to desertification, according to the United Nations Convention to Combat Desertification

The magnitude of the UHI was estimated for each of the four test sites both for the mean monthly period 2002-2008 (Fig. 14) and for selective days of high temperature records of Au‐ gust 2010 (Fig 15). The UHI magnitude was calculated by subtracting the LST value from a rural area (as identified from the position of a pre-selected rural meteorological station) from the respective LST values falling within the urban boundary area of each district on a

Fig.14 presents the mean monthly maximum UHI intensity for the period 2002-2008 for the four urban areas of Cyprus. As noticed, Nicosia, which is located in the centre of Cyprus, is most vulnerable to UHI during the warm period, when the intensity is recorded above four degrees. On the contrary, the other urban areas (Larnaca, Limassol and Paphos), which are close to the coastline, are lesser affected by UHI during the warm period, with intensities recorded around 1.5 to 3.5°C. These areas also demonstrated high UHI intensities during the

Next, the spatio-temporal variation of the UHI intensity for each of the urban areas was ex‐ amined for the period 23 July to 28 August 2010, when high air surface temperatures were recorded (Fig. 14). The temporal variation of the maximum UHI intensity was estimated from the available nocturnal Aqua MODIS images for that period. The results revealed that,

to be better than day time (Rigo et al., 2006).

pixel-by-pixel basis (Tomlinson et al., 2010).

(IACO, 2007)

cold period.

**Figure 12.** Simplified CORINE 2000 Land Cover map of Cyprus

**Figure 13.** Land Surface Temperature map derived from day Aqua pass for the selected heat wave event

#### **6. Urban heat island analysis**

The variation of the UHI magnitude was examined for the four urban areas of Cyprus based on MODIS Aqua images acquired at night-time (at approximately 0130 local time). The se‐ lection of the MODIS Aqua data was based on the criterion that the night-time acquired im‐ ages allow a more precise LST calculation since there is no incoming solar radiation to change the surface radiation balance, while night-time MODIS LST accuracy has been found to be better than day time (Rigo et al., 2006).

**Figure 12.** Simplified CORINE 2000 Land Cover map of Cyprus

16 Remote Sensing of Environment: Integrated Approaches

**6. Urban heat island analysis**

**Figure 13.** Land Surface Temperature map derived from day Aqua pass for the selected heat wave event

The variation of the UHI magnitude was examined for the four urban areas of Cyprus based on MODIS Aqua images acquired at night-time (at approximately 0130 local time). The se‐

**Figure 14.** Areas sensitive to desertification, according to the United Nations Convention to Combat Desertification (IACO, 2007)

The magnitude of the UHI was estimated for each of the four test sites both for the mean monthly period 2002-2008 (Fig. 14) and for selective days of high temperature records of Au‐ gust 2010 (Fig 15). The UHI magnitude was calculated by subtracting the LST value from a rural area (as identified from the position of a pre-selected rural meteorological station) from the respective LST values falling within the urban boundary area of each district on a pixel-by-pixel basis (Tomlinson et al., 2010).

Fig.14 presents the mean monthly maximum UHI intensity for the period 2002-2008 for the four urban areas of Cyprus. As noticed, Nicosia, which is located in the centre of Cyprus, is most vulnerable to UHI during the warm period, when the intensity is recorded above four degrees. On the contrary, the other urban areas (Larnaca, Limassol and Paphos), which are close to the coastline, are lesser affected by UHI during the warm period, with intensities recorded around 1.5 to 3.5°C. These areas also demonstrated high UHI intensities during the cold period.

Next, the spatio-temporal variation of the UHI intensity for each of the urban areas was ex‐ amined for the period 23 July to 28 August 2010, when high air surface temperatures were recorded (Fig. 14). The temporal variation of the maximum UHI intensity was estimated from the available nocturnal Aqua MODIS images for that period. The results revealed that, for most of the cases, the UHI magnitude curves follow a similar trend. Two major peaks were observed, on 31 July and 25 August 2010.

Max UHI intensity (degrees)

23/ 7/ 10 26/ 7/ 10

urban areas of Cyprus, separately

29/ 7/ 10 1/ 8/ 10

sis of Aqua nocturnal data for the period 23 July to 28 August 2010

4/ 8/ 10 7/ 8/ 10 10/ 8/ 10

Limassol Nicosia Paphos Larnaca

**Figure 16.** Temporal variation of maximum UHI intensity for the four urban areas of Cyprus, as derived from the analy-

**Figure 17.** UHI estimated from MODIS Aqua nocturnal images for (a) 31 July and (b) 28 August 2010, for the four

13/ 8/ 10 16/ 8/ 10

Satellite and Ground Measurements for Studying the Urban Heat Island Effect in Cyprus

19/ 8/ 10 22/ 8/ 10 25/ 8/ 10

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28/ 8/ 10

**Figure 15.** Mean monthly maximum UHI magnitude estimated from MODIS Aqua nocturnal images for the period 2002-2008 for Nicosia, Larnaca, Limassol and Paphos

The spatial variation of the UHI magnitude (Fig. 16) was examined for two dates (31 July and 28 August 2010) and was compared to the mean UHI magnitude as calculated for August for the years 2002-2008. The results derived suggest that, in almost all cases, the spatial patterns of the UHI magnitude observed for each urban area are quite simi‐ lar to each other with a few variations in the magnitude of intensity due to the severi‐ ty of the heat wave event. The highest intensities were noticed within the areas of the urban fabric.

The maximum intensities of UHI for each urban area were (a) 31 July 2010: 5.2°C (Nicosia), 3.5°C (Larnaca), 1.9°C (Limassol), and 5.0°C (Paphos) and (b) 25 August 2010: 6.9°C (Nico‐ sia), 3.9°C (Larnaca), 3.1°C (Limassol), and 4.2°C (Paphos). Thus, the deviation form the mean monthly UHI intensities calculated for July and August, correspondingly, were of about 0.6°C and 2.7°C for Nicosia, 0.3°C and 0.8°C for Larnaca, -0.4°C and 1.9°C for Limas‐ sol and 3.2°C and 2.8°C for Paphos.

for most of the cases, the UHI magnitude curves follow a similar trend. Two major peaks

**J FMAMJ JASOND**

Nicosia Larnaca Limassol Paphos

**Figure 15.** Mean monthly maximum UHI magnitude estimated from MODIS Aqua nocturnal images for the period

The spatial variation of the UHI magnitude (Fig. 16) was examined for two dates (31 July and 28 August 2010) and was compared to the mean UHI magnitude as calculated for August for the years 2002-2008. The results derived suggest that, in almost all cases, the spatial patterns of the UHI magnitude observed for each urban area are quite simi‐ lar to each other with a few variations in the magnitude of intensity due to the severi‐ ty of the heat wave event. The highest intensities were noticed within the areas of the

The maximum intensities of UHI for each urban area were (a) 31 July 2010: 5.2°C (Nicosia), 3.5°C (Larnaca), 1.9°C (Limassol), and 5.0°C (Paphos) and (b) 25 August 2010: 6.9°C (Nico‐ sia), 3.9°C (Larnaca), 3.1°C (Limassol), and 4.2°C (Paphos). Thus, the deviation form the mean monthly UHI intensities calculated for July and August, correspondingly, were of about 0.6°C and 2.7°C for Nicosia, 0.3°C and 0.8°C for Larnaca, -0.4°C and 1.9°C for Limas‐

were observed, on 31 July and 25 August 2010.

18 Remote Sensing of Environment: Integrated Approaches

0

urban fabric.

2002-2008 for Nicosia, Larnaca, Limassol and Paphos

sol and 3.2°C and 2.8°C for Paphos.

1

2

3

**Max UHI (deg. C)**

4

5

6

**Figure 16.** Temporal variation of maximum UHI intensity for the four urban areas of Cyprus, as derived from the analysis of Aqua nocturnal data for the period 23 July to 28 August 2010

**Figure 17.** UHI estimated from MODIS Aqua nocturnal images for (a) 31 July and (b) 28 August 2010, for the four urban areas of Cyprus, separately
