To the east of Jamaica and Cuba is the island of Hispaniola. It is the second largest island in the Caribbean, and the largest by population. It is also divided between two separate countries: Haiti and the Dominican Republic. And just as the island is divided geographically and politically, so it is also divided by its temperature data.
To the west in Haiti there is only one station of note in the capital at Port-au-Prince airport, but this is also the only long station on the entire island that has over 1200 months of data before 2014 (all stations in Haiti are listed here). To the east in the Dominican Republic there are six medium stations with over 480 months of data and a further five stations with over 400 months of data (for a full list see here). The locations of all these twelve stations are indicated on the map below in Fig. 109.1. It can be seen that most have warming trends, where a warming trend is defined as one where the temperature gradient for 1911-2010 is positive and exceeds twice the error in that trend, but five have stable or cooling trends. And nine of the twelve stations are located close to the coast. The interior of the island is therefore very under-represented.
Fig. 109.1: The (approximate) locations of the twelve longest weather station records in Haiti and the Dominican Republic. Those stations with a high warming trend between 1911 and 2010 are marked in red while those with a cooling or stable trend are marked in blue. Those denoted with squares are long stations with over 1200 months of data, while diamonds denote stations with more than 400 months of data.
The other distinction between Haiti and The Dominican Republic is in the amount of observed warming seen in each country. The trend for Port-au-Prince airport is shown in Fig. 108.2 below and it clearly exhibits strong warming of over 3°C since 1900 with most of the warming having occurred since 1940. However the data is discontinuous and is not corroborated by any other station, mainly because there are no other stations with enough data locally. In fact it is the only temperature record of any significant length (i.e. over 400 months of data) in the whole of Haiti. It is also from a single station based in the capital city where over 10% of the Haitian population live, so that may also have a strong impact on the trend (e.g. note the difference in trends between Jakarta and the rest of Indonesia shown in Post 31).
Fig. 109.2: The mean temperature change for Port-au-Prince relative to the 1961-1990 monthly averages. The best fit is applied to the monthly mean data from 1916 to 1995 and has a strong positive gradient of +4.18 ± 0.09 °C per century.
In contrast, the Dominican Republic has eleven stations with data extending back to the 1960s or beyond, but none with data before 1940. Its mean temperature anomaly (MTA) over time is shown in Fig. 109.3 below, and while it also exhibits some warming since 1950, it is much more modest at about 1°C. However, this is not the whole story as there are issues regarding data coverage, both geographically and temporally.
Fig. 109.3: The mean temperature change for the Dominican Republic relative to the 1961-1990 monthly averages. The best fit is applied to the monthly mean data from 1951 to 2010 and has a positive gradient of +1.91 ± 0.13 °C per century.
The MTA in Fig. 109.3 was calculated by averaging the temperature anomalies from the eleven longest temperature records for the country. All these records had over 400 months of temperature data before the end of 2013. The anomalies for each station were determined using the usual method as outlined in Post 47. This involved first calculating the monthly reference temperatures (MRTs) for each station using a set reference period, in this case from 1961 to 1990, and then subtracting the MRTs from the raw temperature data to generate the anomalies. If a station had at least twelve valid temperatures per month within the MRT interval then its anomalies were included in the MTA calculation. The total number of stations included in the MTA in Fig. 109.3 each month is indicated in Fig. 109.4 below.
Fig. 109.4: The number of station records included each month in the mean temperature anomaly (MTA) trend for the Dominican Republic in Fig. 109.3.
The data in Fig. 109.4 suggests that the most reliable data in Fig. 109.3 is between 1950 and 1990 as this is where the MTA is calculated using the largest number of stations. Yet the data in Fig. 109.3 suggests that the warming over this interval is negligible (i.e less than 0.2°C) with far more warming occurring in the 1990s where there is much less data. The lack of data for the interior of the Dominican Republic may also play an important factor in affecting the reliability of the warming trend.
Next I calculate the corresponding MTA result based on data that has been adjusted by Berkeley Earth (BE). The result is shown in Fig. 109.5 below and like the raw data in Fig. 109.3 it exhibits a strong warming trend. However in this case, the warming seen for adjusted data is actually less than that seen for the raw data with temperatures rising by only 0.7°C since 1950 compared to about 1°C in Fig. 109.3. This is reflected in the gradients of the best fits in each case with the best bit gradient in Fig. 109.3 being almost 50% greater than the equivalent in Fig. 109.5.
Fig. 109.5: Temperature trends for the Dominican Republic based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1951-2010 and has a gradient of +1.28 ± 0.06°C/century.
Comparing the curves in Fig. 109.5 with the published Berkeley Earth (BE) version in Fig. 109.6 below indicates remarkably good agreement at least as far back as 1950. This indicates that the simple averaging of anomalies to generate the MTA in Fig. 109.3 is as effective and accurate as the more complex gridding method used by Berkeley Earth. It also means that the averaging process cannot be responsible for the difference in trends between that using unadjusted data in Fig. 109.3 and that using adjusted data in Fig. 109.5.
Fig. 109.6: The temperature trend for the Dominican Republic since 1820 according to Berkeley Earth.
The differences between the MTA in Fig. 109.3 and the BE versions using adjusted data in Fig. 109.5 and Fig. 109.6 are instead mainly due to the data processing procedures used by Berkeley Earth. These include homogenization, gridding, Kriging and most significantly breakpoint adjustments. These lead to changes to the original temperature data, the magnitude of these adjustments being the difference in the MTA values seen in Fig. 109.3 and Fig. 109.5. The magnitudes of these adjustments are shown graphically in Fig. 109.7 below. The blue curve is the difference in MTA values between adjusted (Fig. 109.5) and unadjusted data (Fig. 109.3), while the orange curve is the contribution to those adjustments arising solely from breakpoint adjustments. Both show significant fluctuations, but there is a distinct negative trend overall.
Fig. 109.7: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 109.5 after smoothing with a 12-month moving average. The blue curve represents the total BE adjustments including those from homogenization. The linear best fit (red line) to these adjustments for the period 1951-2010 has a negative gradient of -0.62 ± 0.06 °C per century. The orange curve shows the contribution just from breakpoint adjustments.
Summary
According to the raw unadjusted temperature data, the climate of the Dominican Republic may have warmed by as much as 1°C over the past sixty years (see Fig. 109.3). But most of this warming appear to have occurred in the 1990s when there were fewer active stations (see Fig. 109.4). In contrast, there appears to be very little warming before 1990.
Over the same period adjusted temperature data from Berkeley Earth claims to show that the climate of the Dominican Republic has warmed more steadily, but by only 0.7°C since 1950 (see Fig. 109.5).
The lack of data for the Dominican Republic before 1950 and from its interior is a concern.
The data for Haiti comes from only a single station (Port-au-Prince airport) and exhibits much more warming than is seen for the Dominican Republic. It is also discontinuous at multiple times in its history and is uncorroborated by any other data.
Acronyms
BE = Berkeley Earth.
MRT = monthly reference temperature (see Post 47).
MTA = mean temperature anomaly.
List of all stations in Haiti.
List of all stations in the Dominican Republic.
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