Fix links to GRDC pages (#413)

* Fix links to GRDC pages

* Fix link to USGS water services rest API

docs/observations.rst

@@ -6,10 +6,10 @@ The eWaterCycle platform supports observations relevant for calibrating and vali
 USGS
 ----
 
-The `U.S. Geological Survey Water Services <https://waterservices.usgs.gov/>`_ provides public discharge data for a large number of US based stations. In eWaterCycle we make use of the `USGS web service <https://waterservices.usgs.gov/rest/IV-Service.html>`_ to automatically retrieve this data.
+The `U.S. Geological Survey Water Services <https://waterservices.usgs.gov/>`_ provides public discharge data for a large number of US based stations. In eWaterCycle we make use of the `USGS web service <https://waterservices.usgs.gov/test-tools/?service=iv>`_ to automatically retrieve this data.
 The Discharge timestamp is corrected to the UTC timezone. Units are converted from cubic feet per second to cubic meter per second.
 
 GRDC
 ----
 
-The `Global Runoff Data Centre <https://www.bafg.de/GRDC/EN/Home/homepage_node.html>`_ provides discharge data for a large number of stations around the world. In eWaterCycle we support GRDC data. This is not downloaded automatically, but required to be present on the infrastructure where the eWaterCycle platform is deployed. By special permission from GRDC our own instance contains data from the ArcticHYCOS and GCOS/GTN-H, GTN-R projects.
+The `Global Runoff Data Centre <https://grdc.bafg.de/>`_ provides discharge data for a large number of stations around the world. In eWaterCycle we support GRDC data. This is not downloaded automatically, but required to be present on the infrastructure where the eWaterCycle platform is deployed. By special permission from GRDC our own instance contains data from the ArcticHYCOS and GCOS/GTN-H, GTN-R projects.

docs/system_setup.rst

@@ -437,11 +437,11 @@ Download observation data
 
 Observation data is needed to calculate metrics of the model performance or plot a hydrograph . The
 ewatercycle package can use `Global Runoff Data Centre
-(GRDC) <https://www.bafg.de/GRDC>`__ or `U.S. Geological Survey Water
+(GRDC) <https://grdc.bafg.de/>`__ or `U.S. Geological Survey Water
 Services (USGS) <https://waterservices.usgs.gov/>`__ data.
 
 The GRDC daily data files can be ordered at
-https://www.bafg.de/GRDC/EN/02_srvcs/21_tmsrs/riverdischarge_node.html.
+https://grdc.bafg.de/GRDC/EN/02_srvcs/21_tmsrs/riverdischarge_node.html.
 
 The GRDC files should be stored in ``ewatercycle.CFG.grdc_location``
 directory.