Change health system interventions
        https://github.com/SwissTPH/openmalaria/wiki/GeneratedSchema32Doc#change-health-system
        Returns: list of HealthSystems together with timestep when they are applied

def changeHS(self):
        """
        Change health system interventions
        https://github.com/SwissTPH/openmalaria/wiki/GeneratedSchema32Doc#change-health-system
        Returns: list of HealthSystems together with timestep when they are applied
        """
        health_systems = []
        change_hs = self.et.find("changeHS")
        if change_hs is None:
            return health_systems
        for health_system in change_hs.findall("timedDeployment"):
            health_systems.append([int(health_system.attrib("time")), HealthSystem(self.et)])
        return health_systems