Analysis of some extreme temperature indices over Iraq

Climate change has negative impacts on different sectors. Generally, data display significant changes in the properties of extreme events. Daily minimum and maximum temperatures data for 36 meteorological stations of Iraq (1981-2017) were analysed to detect the significant trend and the magnitude trend extreme temperature indices over the 36-year period. RClimDex was used to compute indices and simple regression method was used for trend analysis. The results show that all stations displayed a significant increase in the annual average of maximum value of maximum temperature TXx and the annual average of maximum value of minimum temperature TNx. For the annual diurnal temperature range, about 81.6% of stations have a decreasing trend, while 18.4% have an increasing trend. The TXn index shows 78.9 has a decreasing trend for all stations except 5.3% have no change and 15.8% have an increasing trend. In contrast, the represent of TNn index demonstrate a decreasing trend for 63.2% of stations and 31.6% have an increasing trend fall all stations. Analysis of temperature extremes revealed a significant increase in most stations, which also shows that the country has seen a trend of warming.


Introduction
Climate change it is a fact. Temperature is the most important factor in climate change and extreme temperatures affect our lives more than others. Many studies have revealed warming trends at temperature in the world, but the value of changes are not constant (Jones and Moberg, 2003;Abbasnia, et al., 2016). Global mean of temperature has an increased 0.85 °C over the last century (IPCC, 2013). According to the Intergovernmental Panel on Climate Change (IPCC, 2007) climate change will affect agriculture, increase the risk of hunger; water scarcity and will lead to rapid melting of glaciers in future.
Recent studies of world climate have shown that important changes in temperature happened during the last century. These studies denote that the minimum intensity of extreme temperature has decreased trend (IPCC, 2007). Also the value of maximum temperatures has increased trend (Mohammad et al., 2018). The temperatures indices employed in various studies are arranged by the Commission for Climatology (CCL), World Meteorological Organization (WMO) and the Expert Team on Climate Change Detection and Indices (ETCCDI) who helped several workshops in the globe.
Many studies have studied extreme temperatures and found significant trends in temperature indices (Frich et al., 2002). Annual trends have increased for the maximum and minimum temperatures in Iraq and middle east. Over an increasing trend has been found in extreme temperature indicators over the last 100 years, with a stronger trend in the past three   where, Txkj is the daily maximum temperature in month (year) k, period j.
The monthly (annual) the minimum value of minimum temperature (TNn) is given by: where, Tnkj T is the daily minimum temperature in month (year) k, period j Linear trends of each index at each weather station are computed using linear least square method. This method is a procedure to determine the best fit line to the data. In this study, linear trends with p-value less than 0.10 are considered statistically significant.

Results and discussion
RClimDex relies on the statistical computing environment (R) and provides an easy-to-use interface for calculating extreme climate indicators to monitor and detect climate change. ClimDex calculates all indicators recommended by CCl / CLIVAR. In this study, five temperature indicators were investigated: the maximum value of maximum temperature TXx, the minimum value of maximum temperature TXn, the maximum value of minimum temperature TNx and the minimum value of minimum temperature TNn and Diurnal temperature range DTR. The magnitude of slope have been used to analyze climate variability in Iraq for 38 years. This analysis revealed mainly positive trends in TXx and TNx indicators and negative trends in TNn, TXn and DTR indicators. The temporal distribution of the extreme temperature indices was studied for Iraq. Baghdad station has been chosen to represent the study area. Fig. 2 shows the annual liner trend of extreme temperature indices for Baghdad station. It can be seen that there is a significant positive tren DTR indice indices in Baghdad sta AL-TIMIMI e Fig. 3.   Fig. 4 DTR has a decreasing trend at 32 stations and an increase in six stations in the west region of Iraq (Fig. 5).
The Percentage of annual trends of the extreme temperature indices over Iraq are presented in Table 2. The trends of TXN, TNN and DTR has a negative value (decreasing), while the trends of TXx and TNX has a positive value (increasing).
The warmest day (TXx), warmest night (TNx), diurnal temperature range (DTR), coldest night (TNn) and coldest day (TXn) all display trends consistent with warming. Fig. 6 shows the inter-annual variability of the nationally averaged time serices for TNn, TNx, TXx, TXn and DTR indices. The TNx and TXx indices have an increasing trend over Iraq for the period 1981-2017. The annual mean of TNx index trend is that of 0.0411 °C/36 years. This trend corresponds to an increase of 1.48 °C in the total period analyzed of mean TNn index. Annual mean TXx trend was a little less 0.0385 °C/36 years. The TXx increase corresponding to the total period was 1.38 °C of TXx index. In contrast, the annual mean of TNn and TXn indices have a decreasing trend in Iraq. The annual mean of TXn index trend is that of -0.0238 °C/36years. This trend corresponds to a decrease of 0.0.85 °C in the total period analyzed of mean TXn index. Annual mean TNn trend was a little less 0.0105 °C/36 years. The TNn increase corresponding to the total period was 0.38 °C of TNn index. Also, the difference between daily maximum and minimum temperature DTR in °C was analyzed, the annual mean DTR index has a declining trend in Iraq it was 0.0043 °C/36 years. This trend corresponds to a decrease of 0.15° in the total period analyzed (1981-2017) of DTR index.

Conclusions
The change of extremes temperature associated with climate change has been increasing at most of the stations during the study period . The nationally annual index of the maximum value of maximum temperature TXx and the maximum value of minimum temperature TNx revealed showed an increasing trend at 100% of the stations. For other three indices TXn, TNn and DTR decreasing trends have been detected in most area. The annual mean of TNx index trend was 0.0411 °C/years. This trend corresponds to an increase of 1.48 °C. Annual mean TXx trend was a little less 1.38 °C. The annual mean of TXn index trend is that of -0.0238 °C/years. This trend corresponds to a decrease of 0.85 °C in the total period analyzed of mean TXn index. Annual mean TNn trend was a little less 0.0105 °C/years. The TNn increase corresponding to the total period was 0.38 °C of TNn index. Annual mean DTR index has a decreasing trend in Iraq 0.0043 °C/years. This trend corresponds to a decrease of 0.15 °C for DTR index.